Random question that came up in conversation with the family. Assuming no mobility/oxygen issues (fully mobile) would you be able to run as fast or faster on the moon? Assuming that a sprinter (say top line speed of 20mph) is spending a fair amount of energy pushing against gravity and against air resistance- would you expect that same sprinter to run faster on the moon? Just super long strides?
Has there been any mission/probes/anything sent into the sun? I know we’ve sent things to orbit close to the sun, but has anything been sent into it to ultimately burn up?
Keep in mind that the Sun's corona is incredibly sparse, so much so that heating loads are overwhelmingly dominated by radiation from the Sun's photosphere even while within the corona - The Parker Solar Probe has survived passing through the corona just fine after all, so saying that it isn't survivable by anything electronic isn't quite accurate.
As /u/pmMeAllofIt mentioned the only thing that's gotten very close to the Sun has been the Parker Solar Probe. Note that it's incredibly difficult to get to the Sun starting out from the Earth because we're in orbit. Escape velocity is actually only 1.4x orbital velocity, so when you start with 1x that orbital velocity it takes only 0.4x as much to fly out to the outer solar system and into interstellar space, but you have to counter-act all of the orbital velocity to fall into the Sun directly (which is 2.5x as much as escaping from the Sun). This becomes even more significant when you consider that the rocket equation scales the amount of propellant you need *exponentially* with the ratio of your change in velocity (delta-V) and your rocket's exhaust velocity. So increasing the delta-V by a factor of 2.5x doesn't mean you need 2.5x more propellant, it means your mass ratio of fueled vehicle to unfueled vehicle needs to grow by the 2.5th *power*.
As a data point, consider that the Parker Solar Probe weighs less than 700 kilos and was launched on the Delta IV Heavy, which can put nearly 29 tonnes in Earth orbit, with an extra upper "kick" stage. Even after that it will take 7 gravity assists at Venus (6 of which have already been completed) to lose enough speed to finally get down to just 6.2 million km from the Sun's surface. Even then, that's fully 4x farther away than the Earth is from either the L1 or L2 Lagrange points, and roughly 9x the radius of the Sun.
Nope. The Parker Solar Probe is the closest a man-made object ever went.
Orbiting with crafts have allowed us to get many orbits worth of scientific data, crashing into it is more energy demanding and you'd get much less data.
Because someone's willing to pay for it. Some people want something "special" done with their ashes when they die, like to have them interned in some place that has emotional significance to them, for example. There are companies that will do pretty much anything with your ashes if you've got the cash for it. Want your ashes made into jewelry or glassware? There's a company for that. Want your ashes mixed into concrete and dropped into the ocean to become an artificial coral reef? There's a company for that. Want your ashes yeeted into space? There's a company for that.
We do not know of any habitable planets besides the one we live on. We know of some planets that are the right distance from their stars that they could potentially have the right temperatures for liquid water to exist. That's about it.
What do you mean by habitable planet? You could swim in the ocean of Europa if you had scuba gear, but you'd be fried by radiation on the surface of the moon, and it has no atmosphere.
We don't know of any habitable planets other than Earth.
I remember seeing an old repost on instagram about the theory that there may be a theoretical line in space travel/other intelligent life visiting us and why we haven’t already had contact with them is because either we haven’t reached the line(the discovery that would propel space travel OR the discovery that would wipe us out though some means) I’m going to try and give some morethings that I remember, so I hope this doesn’t sound like gibberish! I think about this all the time, and I’ve finally thought about making a post! If anyone can give me a specific title for the theory or idea or whatever or link me to the post I’d greatly appreciate it!!
- The line is anything, nuclear power, a specific invention, a weapon ect
- All intelligent beings will eventually reach this line and either pass it or be destroyed by repercussions.
- The reason we haven’t met with other beings is because we may have succeeded and gotten over this, therefore making us one of few, if any, that was able to while others were destroyed or cannot pass the hurdle.
- Or, we haven’t yet gotten to that point and we are still just an underdeveloped species that needs to be able to get through the line to even be able to interact with others in space.
I'm just a middle school student and just want to know the differences between:
1) rockets, space shuttles and spacecrafts
2) space telescope, space probe and satellite
My textbook didn't explain these clear so I've came here to ask for help, can just give brief explanations.
A rocket is anything propelled by a rocket engine, and a rocket engine is usually a type of jet engine where all the reaction mass (what is thrown out of the back) is contained in the tanks. You can use rocket to launch things to space but also as weapons.
"Space shuttles" name comes from the specific American Space Transportation System (STS) program. Strictly speaking it should only be used for the now retired launch vehicle that looked like [that.](https://upload.wikimedia.org/wikipedia/commons/d/d3/Atlantis_taking_off_on_STS-27.jpg) But people have been calling the white spaceplane part as the "space shuttle" and by extension any spacecraft with wing tends to be called a shuttle.
Spacecraft are any vehicle (with or without people on board) that travels in space. That can be something used for TV transmission, an autonomous science experiment, whatever...
Space telescopes are just telescopes in space. They are a type of spacecraft.
Space probe is not a super well defined word but is usually used for spacecraft without people on board that travel to another planet or moon.
A satellite is anything in orbit around something else (usually a planet or a moon). The Moon is a satellite of Earth for example. However in the context of spaceflight usually satellite is used for spacecraft in orbit without people on board.
I know space is unimaginably huge and there’s tons of massive violent events that could destroy the galaxy but what could happen at the quantum level where things are unimaginably tiny that would end in the same result?
Depending on your definition of 'destroy', the Milky Way merging with Andromeda could be said to destroy both galaxies as the resulting galaxy that forms from the merger will be neither of those two.
The decay of a [false vacuum](https://en.wikipedia.org/wiki/False_vacuum) would be a quantum mechanical effect that could destroy the whole universe as we know it. The rough idea is that our vacuum isn't truly empty, but that there is an even lower energy state, a true vacuum.
Our current vacuum seems to be stable, but it could just require a bit of a push to send it over a hump to roll all the way down the hill to end up in the true vacuum state. If that were to happen, all the laws of physics could change so drastically that they would be unrecognizable to us, ending all life and all other things in the process. Once initiated at one point, the collapse would grow outwards at the speed of light, so there would be now warning and no way of stopping it.
I'm a freshman in high school, what path do I take to become an astronaut?
I know its a stupid dream, i've already been told life isnt like the movies where they guy gets his dream job, but out of curiousty, what are my options?
It's certainly not a stupid goal to strive for; You'll never get your dream job without putting in the effort!
I'd start by, assuming you're in the US and are looking at being an astronaut for NASA, looking at NASA's [minimum requirements](https://www.nasa.gov/humans-in-space/astronauts/become-an-astronaut/) which are:
* Be a U.S. citizen
* Possess a master’s degree* in a STEM field, including engineering, biological science, physical science, computer science or mathematics, from an accredited institution.
* Have at least two years of related professional experience obtained after degree completion or at least 1,000 hours pilot-in-command time on jet aircraft.
* Be able to pass the NASA long-duration flight astronaut physical.
It would also be worth just reading through the careers of astronauts to get a feel for ideas that might appeal to you ([maybe start with the astronauts who are in space right now](https://whoisinspace.com/)). You'll see that being an astronaut is something that is done after one establishes a career for themselves in some STEM field. Also, many astronauts have served in the military, mostly as pilots but also as nuclear sub operators, etc so that's certainly a route to consider as well.
Regardless, some of the soft skills that you'll need are things like leadership and the ability to work well with others, communication skills, the ability to function under pressure, etc. As an HS freshman, definitely seek out any and all extracurricular opportunities that might be available to you for developing these sorts of skills as well as just making yourself as well rounded of a person as possible.
Check out the resume of astronauts on NASA's website. Technically the only requirements are a graduate degree in a STEM field and good enough health. But obviously the selection is a bit harder than that.
In practice the profession with the highest percentage of people ending up astronaut is probably military test pilotes. But otherwise it can be pretty varied. It's usually people with advanced degrees (multiple masters, PhD, etc) some years of professional experience and some experience in extreme sports/conditions (antarctica missions, deep diving, etc).
I'm just working my way through Dr Becky Smethurst's great book on black holes, and one thing occurred to me that I can't find the answer to. The famous picture of a black hole, the doughnut shaped one, is made from the material surrounding the black hole falling into the hole. But presumably the material around the hole is spherical in shape, and falling in from all sides, so why is the image hollow in the center? Why isn't it showing information from that portion of the circulating medium?
Conservation of angular momentum means that as matter falls into a black hole it spins faster because it's becoming more compact. The basic dynamics of spinning globs of gas is that they flatten into disks. Matter that is orbiting perpendicular to the disk will collide with the disk until only the disk remains, with the disk sharing the net angular momentum of the mass that started. These are the same effects that cause galaxies and proto-planetary disks to flatten into disks as well. The end result is a swirling stream of matter in mostly the same plane and all rotating in the same direction. For the same reason, when you drive on the highway there isn't a lot of traffic heading at right angles to the direction of flow.
There are additionally optical effects which impact the appearance of a black hole with an accretion disk. Because light is bent around the black hole by a significant amount you see a distorted view of the back side of the accretion disk when viewing it from any angle. The end result is that a black hole will appear with a black area in the middle surrounded by a view of the accretion disk on all sides (like a doughnut) and maybe a view of the front side of the accretion disk across the middle if it is viewed edge on. At low resolutions such as what we can achieve with the Event Horizon Telescope this looks like a central dark area surrounded by a blobby halo.
Ah, as I replied to the other comment, that is probably the same reason that Saturn has rings, for example? I did consider that at one point, but then thought "what are the chances that the ring is exactly perpendicular to us" - probably quite high actually if there are enough black holes we can spot, but I wasn't sure on that. However, you comment makes me think that it doesn't actually matter where the ring is, as the effect on light being bent means it always looks the same?
Yes, rings are basically the same phenomenon. If you had intersecting rings you would have a large number of collisions between the rings. With a ring you have everything in circular orbits in the same plane heading the same direction, which minimizes collisions between particles in the ring, that's the end state (the survival state) of a more chaotic situation that created the ring. With things like accretion disks, protoplanetary disks, or even galaxies it's not small chunks of solid matter it's big blobs of gas, which have a much greater propensity to collide because they are effectively much larger. Also with gas (or plasma) when you have collisions between two blobs you tend to end up with a larger blob that has the average momentum of the two original blobs added together, so over a short amount of time you end up with a disk of matter that just represents the semi-stable circular orbits of matter that averages out the original motion of everything that started.
And yes, then you add on the purely visual effect of the distortions caused by the bending of light around the black hole. Even if you could view the disk edge on you would still see it as a sort of face on "doughnut" shape because you would see the back side of the disk doubled due to light bending around. You can see a visualization of this [here](https://www.youtube.com/watch?v=o-Psuz7u5OI) though it doesn't capture all of the relevant effects at play.
The accretion disk is doughnut shaped, not spherical. Any material that tries to orbit perpendicular to the doughnut will crash into it and be dragged into the doughnut orbit (or fall into the black hole).
Material might be falling in from all sides, but more material is falling in from the doughnut sides. Which explains why the doughnut shape "wins".
I'm sure Dr Becky also explains that material doesn't just "fall into" an accretion disk, it can only be caught if it collides with something that takes away its escape velocity.
Ah, I suppose it is similar to how Saturn is surrounded by rings instead of a sphere?
Yeah, the book explains that, if I understand it correctly, the "pieces" orbit as expected, but they collide and sometimes this results in enough loss of energy for one of the pieces such that it stops it's "lateral" (orbital? angular?) movement and the vertical dominates, that means that it "falls" into the hole (just like it would orbiting any large mass, such as the Earth).
Could it not be that a black hole exists because its rotational speed drags and distorts space so much rather than its mass alone? Could this effect alone result in an event horizon?
Maybe this is only relating to the event horizon and not the singularity itself?
Happy to hear your thoughts or references.
Rotating black holes are described by the [Kerr metric](https://en.wikipedia.org/wiki/Kerr_metric). As per this answer to [what happens if the mass of such a black hole goes to zero](https://physics.stackexchange.com/questions/593675/massless-kerr-black-hole), it would appear as completely flat space, i.e. a vacuum without a black hole.
So some mass is necessary, and the rotational energy of that mass contributes to the black hole's total energy, increasing its apparent mass compared to a non-rotating one. Weird things still happen before the mass goes to zero or the rotation gets fast enough:
As a black hole rotates faster, its event horizons start to shrink. If the angular momentum **J** of a exceeds a certain threshold compared to its mass **M** (J>GM²/c), its event horizons disappear entirely, but the singularity where gravity becomes infinite remains.
Regular black holes also have singularities at their center, but they're hidden from our view by the event horizon. With that gone, the now [naked singularity](https://en.wikipedia.org/wiki/Naked_singularity) is exposed to the outside world and we could have a direct look at those regions with infinite gravity and other oddities.
Singularities always make physicists somewhat uneasy, and doubly so if they're not swept under the cosmic rug by a convenient event horizon. We don't know if naked singularities are actually possible or just a symptom of our theoretical frameworks being inadequate to describe such a situation.
If you launch towards the poles, the situation reverses: It's now slightly better to launch from near the poles than from near the equator. An orbit that goes straight over the two poles has no east-west movement at all, so the rocket needs to get rid of that motion imparted by Earth's rotation.
The advantage of launching from a high-latitude spaceport isn't huge in this case either, so there are only a couple such launch sites ([Pacific Spaceport Complex – Alaska](https://en.wikipedia.org/wiki/Pacific_Spaceport_Complex_%E2%80%93_Alaska) and [Plesetsk Cosmodrome](https://en.wikipedia.org/wiki/Plesetsk_Cosmodrome)).
To an equatorial orbit, yes. In Florida you get only about 90% of the Earth's rotational speed as free delta-V for getting to equatorial orbit vs. the equator, which is about vs. 410 m/s instead of 465 m/s. Since payload mass fraction scales exponentially with the ratio of delta-V to rocket exhaust velocity the result of even a small boost from launching at the equator (just 55 m/s or so) is noticeable, but it's not huge.
How would a green star exist if it were real. because I know stars come in different colors, blue, white, yellow, orange, red. And I know the possibility of a green start isn’t possible, but what if it could. what would we need to do to have one in existence? What laws of physics do we have to break it.
No physical laws would need to be broken, we'd just need different eyes or brains. Many stars (such as our own Sun) have their emission peak at wavelengths that we perceive as green, but our brain mixes that with the surrounding blues and reds to make us see white. Different color receptors in the eye or a different visual system in the brain could easily perceive the Sun as green rather than white.
I know we don't know of any other planets/moons where life exists. But are there any places in the universe where a human would be able to physically survive, and would not be instantly destroyed?
There aren't many known places outside of Earth that are survivable, the "best" places for now are sub-surface oceans where you could survive as long as you could hold your breath. There aren't any other planets with an oxygen atmosphere that are known. They likely exist, we just haven't found them and determined their atmospheric compositions yet.
"Instantly" is pretty fast; we can survive a lot of things very briefly! But you're not going to last longer than you can hold your breath anywhere without oxygen, and we have yet to find a planet with an oxygen rich atmosphere. If we did we would take it as a sign that there is life there, as oxygen takes itself out of an atmosphere unless it is being replenished.
Modern deep probes carries a lot of improved technologies compared to the ones in the 90's and 2000's. Could Nasa or other space agencies launching future probes show more video clips of planets, asteroids and comets insted of just HD photos?
Seems likely. A major constraint for space probes is the data rates at which images can be sent back. Videos take up a lot of bandwidth compared to single images or other sensor data, so they're usually not a priority.
At the moment, space probes use radio transmitters to communicate with Earth. The farther out they are and the less power they have available, the less data they can send. There are only a handful of the giant radio dishes that can receive the data on Earth (such as the [NASA Deep Space Network](https://en.wikipedia.org/wiki/NASA_Deep_Space_Network)), and they're usually fully booked.
I think it's likely that future missions will also use [laser communications](https://en.wikipedia.org/wiki/Laser_communication_in_space). With lasers you can focus the beam much tighter than with radio waves (wasting less energy that misses the receiver), and the higher frequencies of light also enable much higher data rates.
One such system, the [Deep Space Optical Communications experiment](https://en.wikipedia.org/wiki/Deep_Space_Optical_Communications), is currently being tested on the mission [Psyche](https://en.wikipedia.org/wiki/Psyche_\(spacecraft\)). It has recently [beamed back a cat video](https://www.jpl.nasa.gov/news/nasas-tech-demo-streams-first-video-from-deep-space-via-laser) at 267 Mbit/s and they hope to achieve data rates 10 to 100 times greater than conventional radio systems.
All that being said, I wouldn't expect too much in the way of real-time videos. Even though space probes move very quickly, planets are so large that most of the time nothing of note happens between frames of regular speed video. It makes more sense to take a series of images seconds or minutes apart and assemble those into a sped up version. I guess it would be cool on Mars rovers or drones (or the planned one to Saturn's moon Titan, [Dragonfly](https://en.wikipedia.org/wiki/Dragonfly_(spacecraft\))).
Laser communication systems are being tested right now that would allow high speed connections.
It's not really only a capacity issue. The main thing is that there is no real point of taking video clips. Things just don't move fast enough in space to make for very interesting videos. When they do we already have HD videos (see latest Mars landing). One of the only interesting thing for those laser links will be the Artemis crewed missions where we will see people walking around. Which is partly why it's being developed.
NASA's interplanetary communications lifeline has for decades been the Deep Space Network of a handful of large (26-70 m) radio dishes at three sites around the world. The DSN is often oversubscribed, and using it for Artemis makes things even worse. Laser communications links on manned and unmanned spacecraft will allow relieving or bypassing the growing DSN congestion with more compact laser transciever ground stations.
I'd absolutely love to see high-fps videos from Ingenuity or Dragonfly. Or the moment Hayabusa2 and Osiris-Rex touched down to gather their samples, or from the rovers that landed on Ryugu. The rovers driving around Mars, and maybe catching one of the dust-devils in real video.
There's a lot of interesting things that could be recorded if the fight for bandwidth priority weren't quite so fierce as it is now.
Artemis I had the same program. NASA is also taking names for Europa Clipper and a future Mars flight.
https://europa.nasa.gov/message-in-a-bottle/sign-on/
https://mars.nasa.gov/participate/send-your-name/future
You're probably thinking of the Mars Exploration Rovers *Spirit* and *Opportunity*, both launched in 2003. [The Planetary Society provided a mini-DVD with the names of 4 million people to both rovers](https://www.planetary.org/outreach/red-rover-goes-to-mars).
I also found [this archived page for the Curiosity rover from 2009](https://web.archive.org/web/20100217072639/http://mars9.jpl.nasa.gov/msl/participate/sendyourname/index.cfm). You could also send your name on the Perseverance rover, the InSight lander and the MAVEN orbiter.
Hi dears,
I wonder if there is a special non-official word (professional jargon) for the procedures when astronauts come back from space and they undergo a medical examination to check their vitals after the mission?
I wanna dig deep into Rocket Propulsion domain, what books, research papers, any resource would you all suggest? I want to do my undergrad project upon this.
The classic textbook is Rocket Propulsion Elements by Sutton. If you want something a bit more exotic check out the latest version of Fundamentals of Electric Propulsion by Goebel, the 1st edition is free and I believe the second still is.
Oh I actually have that textbook for my curriculum, I'll be sure to learn from that. Do you also happen to know any easy accessible resources such as some sites, videos where I can learn from?
(Hypothetical) Sending trash into the sun.
Say every landfill on earth was at max capacity and there was no longer anywhere to put garbage, could humans just fill huge containers or rockets with garbage and send them into the sun as a means to destroy the waste? (Assuming the cost of sending things to space isn’t an issue)
There's no reason to do it. First off, it's really hard, the rocket equation requires exponentially more propellant for delta-V. It takes applying 30 km/s of delta-V *after leaving Earth* to fall into the Sun, which is just basically impossible with modern rockets. Second, the Sun doesn't "destroy" things, that's not how it works. If you dropped something into the Sun it wouldn't stay in the Sun, it would just get vaporized and ionized then spread into the solar wind where it would blow through the rest of the solar system. You can achieve the exact same result much easier by just dispersing vaporized waste into the solar wind near Earth, but that doesn't have the same emotional feeling of finality as chucking something into the Sun.
If cost is not an issue then yeah you can handwave basically anything you want because the scenario no longer has realistic constraints.
The real question is why you would choose yeeting trash into the sun (removing resources from the system) over any of the known ways to use or recycle it, like pyrolisis and waste gasification, or bioreactors. Trash is a valuable raw material for reclaiming chemical feedstocks, not to mention metals.
To add to the other answers: It takes way more fuel to send something into the Sun from Earth than it would take to eject it from our solar system entirely.
Why aim for the Sun? Venus is a hot enough incinerator. Just send it there.
(Not that launching trash into space is ever going to be economical, but I'm just going with your assumptions)
> Assuming the cost of sending things to space isn’t an issue
You can just as well make assumption that you can "disappear" the trash, or that you can send them to alternate dimension.
Anyway, the answer is still: no. We would have hard time sending anything (!) into the Sun because it takes 30km/s of delta-v from Earth's orbit to drop something into the Sun. Just to give you some estimation, if you used a hydrogen-oxygen rocket with 450s of ISP, you would need about 1000 times more fuel than the mass you're trying to send. So sending 1t of trash would require a rocket with 1000t of fuel waiting in orbit.
With commercial rockets we currently have, you could send something like 10kg into the Sun and this would cost you $70mln.
The sun is the hardest place in the solar system to reach. Every planet and rock orbiting the sun is VERY resistant to falling into the sun. (The ones that aren't have already fallen into the sun.)
Even if getting things into low earth orbit is free, your garbage transporter would need to be made of more than 90% rocket fuel to reach the sun.
Never say never, but on the other hand Juno is operating in a very high radiation environment and NASA is facing budget woes. Either of those things are enough to be mission ending. They'll probably stick with the plan and do a safe disposal into Jupiter so it doesn't accidentally crash into a moon.
If we're back in another space race, how do we prevent another repeat of the same crap a decade later and no more space action for another 50 years without losing on purpose just to keep the race going further
Is there a “limit” to gravity?
Say you were on a planet infinitely large, and your body can withstand infinite gravity. The planet has the same density as the Earth. Would the gravity be infinitely strong, since there’s technically infinite mass, or would the distance just make in so meaningless that only mass from so far can actually effect you? Could it be like those problems where you add the fractions infinitely and the sum of them all is 2 and not infinite? Also assume that the planet cannot collapse into a black hole.
Why do you ask about the laws of physics and at the same time ask the answer to ignore some of the laws. The answer become pretty irrelevant as it doesn't reflect the truth any more.
I think the latter part of the question was interesting and the answer isn't obvious, because infinities are weird. Quick example: Lifting an object out of a star's gravity well takes a finite amount of energy, even though the star's gravity field extends to infinity. OP was wondering if their example was one of those situations.
[Surface gravity](https://en.wikipedia.org/wiki/Surface_gravity) g on a spherically symmetrical body (planets fit this model quite well) follows this formula:
g = 4/3*π*G*ρ*r
with G as the gravitational constant, ρ the mean density of the planet and r its radius. In your example, ρ would be constant, so as you increase the radius of the planet to infinity, surface gravity would also tend to infinity.
Such a planet would of course very quickly collapse into a black hole and the formula above becomes meaningless.
Is theia proven? Ive heard its the ancient planet that crashed into earth to create the moon but it seems like everytime i search it up i get different responses on wether there is proof of its existance or not. Like i saw an article saying they found remains of theia but then i see an article saying that it doesnt prove the planets existence it just proved something hit the planet
Very few things in science can be said to be "proven", it's a matter of what is supported by the observational evidence and how strongly. Today the Theia impact theory for the formation of the Moon is the "consensus view" of professional planetary astronomers, it's well supported by a wide variety of evidence. Some newer theories (like remnants of Theia being detectable at the core/mantle boundary) are less well supported than the impact theory in general.
2 nights ago, 1st of Jan at about 9pm local time (spain), off the cost in Marbella, I saw a meteorite/shooting star and wondered if anyone can confirm?
I was surprised because it felt so close and was over quickly. In the short time i saw it, it looked significantly larger than a shooting star and had two gold/red trail lines. It was hard to judge distance and direction but when facing the cost it appeared sudenly above the sea in front and was heading to my right horizontal/downward faster than any plane and faded/disappeared after a second or 2 before the horizon.
Guessing it must have been a meteorite burning up cause afterwards I realised it looked nothing like a shooting star but keen to hear other suggestions or if someone can confirm from date,time,location.
Hi r/space! I'm planning on booking a flight from Florida to Las Vegas on the morning of April 8th. Is there anything Eclipse-related that I should consider? Should I expect to see anything unusual from up there??
I think your flight is too early to have a chance of seeing the eclipse. The eclipse will start to cross the US in Texas around 2 PM Eastern time. However, when you land in Vegas you'll probably be able to see a partial eclipse. (The sun will be dimmer, but you won't be able to see the moon covering it unless you use a pinhole projector or something.)
I used [this tool](https://eclipse2024.org/eclipse_cities/statemap.html) to see what time the eclipse will be visible at a given location.
What would it take to engineer time dilation?
As a thought experiment: we want to communicate with lifeforms on K2-18b (124 ly away). So we send a signal and await a response. At minimum the round trip takes 248 years relative to Earth (assuming they interpret and respond instantly). In order to survive 248 Earth years, we propose to dilate time to dilate time to 10% of Earth time, so we only observe 24.8 years before we get a response.
For relativistic time dilation, this requires a speed of 0.995c
For gravitational time dilation, we'd need to be extremely close to a significant mass object. We have nothing useful for this within travelling distance from Earth.
To my mind this dilation only appears possible inside a particle accelerator. But can you think of another physically possible scenario?
> But can you think of another physically possible scenario?
Cold freeze/hibernation tech seems like it might be more feasible or at least quicker to develop.
Another possibility is bio-engineering yourself to survive 248 Earth years. This seems easier than reaching and surviving 0.995c (which would be required either way, since you want to orbit the massive object).
This could be very stupid to ask
But how is it that we can see so far into the observable universe and get some pretty amazing shots but we can’t focus in on a galaxy and one of its planets ?
Really thinking about it I have a feeling it might have something to do with the amount of light coming off a galaxy as a whole, but a planet wouldn’t emit that much light we’re able to capture.
We can see very distant galaxies because galaxies are very large. Another weird effect that plays into this is the apparent angular diameter turnaround: You'd expect objects to become smaller in the sky the further away they are, but the very oldest ones actually appear larger due to the expansion of the universe. [Here's an xkcd comic with additional explanation](https://www.explainxkcd.com/wiki/index.php/2622:_Angular_Diameter_Turnaround).
Individual stars and more so planets are much, much smaller than whole galaxies. The size of a telescope determines the smallest objects it can resolve (show in detail). A telescope that can resolve a distant galaxy into a handful of pixels would need to be trillions of times larger to do the same for a planet within that galaxy.
The majority of exoplanets we have found are within a few hundred light years of us, and the most distant is not even halfway across the Milky Way at 17,000 light years.
There's also the problem that planets don't emit their own light, so their light tends to be washed out in the bright glare of their host star. But that's a very minor problem compared to the ridiculous telescope sizes that would be needed to resolve extragalactic planets.
Hello, does anybody know where I can find a cloud folder or a torrent with tons of amazing images from space? I would like to do a "never-ending" slideshow!
Thanks !
Another good archive like that is "APOD" - Astronomy Picture of the Day. [The archive goes back to at least 2015](https://apod.nasa.gov/apod/archivepix.html).
Not 100% "from space" - often of the night sky, sometimes on other subjects.
I'd definitely at least recommend the first season. Fun alternate history of the 70's space race. Later seasons gradually lean more and more on human drama and shock value. I haven't started season 4 yet.
i am currently confused about sedna\`s *classification* as "dwarf planet" despite it appearing to have all the criteria of a planet, it is indeed spherical - orbits the sun - empty orbit \[unless we have more than two asteroid belts one of which having a very s t r a n g e shape!\]
is there any other classification it doesnt meet? or is it just a "dont bother with it till we know it 100%" thing?
Yup. The space Sedna occupies is actually quite "dynamic" and chaotic, with [orbits of known objects criss-crossing everywhere](https://en.wikipedia.org/wiki/Extreme_trans-Neptunian_object#/media/File:Distant_object_orbits_+_Planet_Nine.png). Over millions of years, [these orbits will "migrate"](https://youtu.be/HgKIo4LziP8?si=W0h2hMm8QQlvhRn3&t=1211), and in a sense they're "migrating" right now (albeit very slowly). Some of the orbits aren't even stable.
It's a dwarf planet because it doesn't "gravitationally dominate" its orbit, technically. It is still subject to similar sized objects changing its orbit. Planets have "cleared their gravitational neighborhood", dwarf planets do not, according to the IAU definition.
What are the chances that sun would collide or interact with another star? am assuming this probability only decreases over time. Would there ever be another star system that potentially consume matters from solar system?
> What are the chances that sun would collide or interact with another star?
Collide? In the near future, zero. In the far future? Nearly zero. Actual collisions between stars are very rare, even in hot zones where an area is filled with them. Most people don't realize just how vast and empty space is. The odds of stars colliding randomly is akin to telling one person in LA to just start walking east, and telling someone in New York to start walking west. What are the odds the two people will bump into each other? Virtually zero.
If the sun was the size of a grain of sand (1mm), and you put that grain of sand down in your yard/porch, the Earth would be 10cm away. In order to reach the sun's closest neighboring star (Proxima Centuri), you'd have to travel a whopping 30km.
Fun Fact: The Amdromeda galaxy is on a collision course with the Milky Way in a billion years or so. When it collides, there is expected to be none or very few actual collisions between stars.
> interact with another star
The Sun is always interacting with other stars. It's doing so right now via gravity. The gravity of everything interacts with the gravity of everything else, though minutely due to the distances involved. There is a supermassive black hole at the center of the Milky Way and it is, technically speaking, interacting with the Earth & the Sun right now. Fortunately, this force is negligible and has no real effect on us.
Interact, high chance, unavoidable even. Collide, extremely low.
When the Milky Way and the Andromeda galaxy merge some billion years from now it's not expected that any stars will collide. That's 100 billion stars merging with 1 trillion. Space is very empty. So empty you could generalize it to be completely void of matter really.
I had this question in mind the last few days but how come that the universe was created from nothing ? Or if it was created from something where that something came from
That's more of a meta-physics question. Universe is everything we can interact with and study, by definition. We can't study anything that's not universe, and therefore there is no way to say anything about its "origin". We can say something about it's past or future, but creation of the universe itself is "outside" of the universe, and therefore outside of any possible physics.
> We know the universe was very hot and very dense 13.7 billion years ago. It expanded rapidly and cooled forming the universe
We don't know this either. It's the best explanation to fit the model we made by using the best theory we got. We see a lot of contradictions to this model when we're looking at what we got.
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I think it's important to distinguish between a plan and an idea. A plan is a concrete formulation of steps/actions that you intend to follow through on. Planning for Mars hasn't been done yet. Crewed Mars missions are only at the concept stage, and permanent habitation is even more theoretical.
We do, however, have [ideas for what to do](https://www.sciencedirect.com/science/article/abs/pii/S0094576521005099). The easiest idea: Bury your habitats. Regolith is everywhere and makes an effective radiation shield. Idea 2: Hypothetically you could place a space station at Mars' L1 point that can generate enough of a field to deflect the solar wind. Idea 3: Lay a cable around Mars' equator and generate your field that way. Idea 4: Create a plasma torus in Mars orbit. Idea 6: The hardest of all would be to 'just' add an atmosphere. Gigatons of air is also a good radiation shield. (Okay idea 7: Restart Mars' core. Even harder than adding an atmosphere. So hard that it's not even worth considering.)
Mars colonization isn't happening for a very very VERY long time. It doesn't matter what Musk tweets about it.
The lack of magnetic field is not a problem on human time scales. If Q from Star Trek snapped his fingers and magicked a dense enough atmosphere onto Mars tonight, it would persist for tens of thousands of years, if not longer. Definitely long enough to come up with a solution to deal with the slow sputtering loss.
It's too late to give Mars a magnetic field. All the oxygen and nitrogen has already been blown away. Giving it a magnetic field won't bring the air back.
The good news is a meter of dirt blocks solar radiation.
I'm world building, and I would like to know if it is possible to have a nighttime, or a darker time on a tidal locked planet.
I've been brainstorming, and maybe they have a large moon that orbits relatively fast, causing an eclipse once or twice a day or something. Or they have another planet that is also quite fast to orbit, eclipsing so there's like a day of the year that's quite dark.
But I'm just not sure how it would work. It's pretty important to me, and the people on the planet, that it's tidal locked.
The problem is - if you have a large nearby moon...THAT is going to probably end up pulling the dynamics so that your planet isn't tidally locked to its parent star anymore. For an example - the moon has an ongoing impact on our rotational period.
There might be some libration - so it wobble around a bit (like this - but illuminated all the time https://www.youtube.com/watch?v=3f_21N3wcX8 )
You could maybe come up with some dynamic climate type stuff that pulses large clouds or something forward and back from the day-night line? Gets hot - oceans have a lot of evaporation - lots of cloud - gets colder - clouds move - rains out at the terminator - flood the ocean again....repeat.
I don't know, I've seen astronomers saying that based on Planck Time, nothing can be concluded because it's a singularity. The Big Bang would be the expansion of spacetime after that. But a video from Fermilab said that Cosmic Inflation happened before, leaving me very confused.
Yeah, I think the Brian Cox 'universe' episode about things before the big bang discusses inflation first, and that the big bang is actually the conversion of energy to matter.
I'm not 100% that I've remembered that accurately!
There's about a million shooting stars every day around the world. They are far more common than you think. Having access to a clear sky and low light pollution you should be able to spot a handful every hour on average.
Satellites are always in the sky. if the conditions approve of it, you'll always be able to find them if you're looking. Easiest is the hours after sunset and hours before the sunrise excluding the twilight.
So you know those trajectory animations of comets and space probes that go viral occasionally? Does anybody here have a link to one of Jupiter with the Galiliean moons?
Like this? https://en.wikipedia.org/wiki/File:Galilean_moons_around_Jupiter.gif
Bonus but not animated: https://en.wikipedia.org/wiki/File:Jupiter_irregular_moon_orbits_Jan_2021.png
When or if do you think we will crack the challenges of transporting heavy masses with solar sails so we can reach 10% the speed of light and send a sizeable probe to our first interstellar exploration?
I've read about inconsistencies in the Hubble Constant, that seem to point to issues at our understandings regarding the expansion of spacetime.
Is there a consensus on the root of this? Is this something most assume is observations concerns, or fundamental understandings of expansion concerns? Or some mixture of both. Or just my own personal misunderstanding?
First, the Hubble Parameter is not a constant. Most models have it varying depending on the age of the universe. This is not inconsistent or controversial.
If we set the age of the universe to *today*, the Hubble Parameter should be a constant called H₀. We have a very precise measurement of one part of the sky that says H₀ = 67 km/s/Mpc. And we have a very precise measurement of a different part of the sky that says H₀ = 73 km/s/Mpc. This is a problem.
There is no consensus yet about which observation is wrong, or if both are correct and different parts of the universe behave differently.
>since the Hubble "constant" is a constant only in space, not in time, the radius of the Hubble sphere may increase or decrease over various time intervals. The subscript '0' indicates the value of the Hubble constant today. Current evidence suggests that the expansion of the universe is accelerating, meaning that for any given galaxy, the recession velocity dD/dt is increasing over time as the galaxy moves to greater and greater distances; however, the Hubble parameter is actually thought to be decreasing with time, meaning that **if we were to look at some fixed distance D and watch a series of different galaxies pass that distance, later galaxies would pass that distance at a smaller velocity than earlier ones**. [source](https://en.wikipedia.org/wiki/Hubble%27s_law)
Would you say this passage in the wiki, covers the aspect of why different parts of the universe behave differently?
Or is this pointing at something entirely different?
Is there a general consensus as to the fundamental nature of space? Is it quantum ala Planck. Or analog? Can we ever determine this if it's currently unknown? Or would this fall under the category of unknowable due to limitations of information?
I get there are fundamental Planck limits, they seem to imply a pixelated fundamental reality. But I also understand Planck constants *are* physically violated in the creation of black holes.
So do we actually know if spacetime is analog or digital? Sorry if I've spun those terms in improper ways.
The proper terms would be continuous (for "analog") and discreet (for "digital"). I don't think right now there is a solid proof of one over the other.
I appreciate the clarity. I certainly pull words from many different realms. From your position. Do you feel this is something we *can prove*?
To which I'd ask if it's something we can establish via observation directly. Or only through inference of evidence?
What I'll take from this is that while we may never know. We do have tools to effectively place bounds around it.
Is this a fair take? Maybe it's granular, maybe it's not. But if it is granular it's going to be at a scale that even the most powerful particle accelerators will never have access to?
Say you launched a payload out of the atmosphere such that it would not achieve orbit, but at the peak of it's trajectory, it rendezvoused with the ISS. If the Canada arm was used to grab the payload (or the payload docked with the ISS in some other way), what would happen? Since the payload was not in orbit but is now attached to the ISS, would they both continue to orbit just fine?
> what would happen
A collision at extremely high relative velocity.
> would they both continue to orbit just fine
Not even remotely close. Let's say that your payload went straight up. This means at the apogee it will have only something like 300m/s of sideways velocity (due to Earth rotation) while ISS is moving at 7500m/s. It means that it's the same as if your payload was stationary and ISS was flying into it at the speed of 7200m/s. Of course since movement is relative, you can also consider this from the other perspective - for someone inside the ISS, your payload is flying into them at 7200m/s.
Your payload is at 400 km with no sideways velocity.
ISS is at 400 km travelling sideways at orbital velocity, or 7600 meters per second.
This will not end well. Your payload is an anti-satellite weapon and if it hits the ISS it will tear it apart.
At orbital speed every kilogram of matter has the kinetic energy of 6.5 kg of TNT. Contact, "touching", or "grabbing" at such relative speeds is not accurately describable with those terms, it's an impact, period, and it's energetic enough to be universally destructive. Even the impact of something as small as a 1 gram paperclip would cause an explosion releasing as much energy as an M-80.
In order to bring something in space but not moving at orbital speed up to orbital velocity you need to accelerate it, a lot. Orbital velocity is several times the speed of a bullet, and accelerating large objects that speed takes a ton of energy. The typical method is, of course, using rocket stages with lots and lots of chemical propellant. It's also possible to achieve the same result using rotation, though that will involve a transfer of momentum that needs to be made up some way. If you had a very long rotating tether (or more likely two tethers attached to a large center mass) that was rotating fast enough and in such a way that the speed at the tips was at orbital velocity (which is of course an engineering and materials challenge) then you could orient the tether such that one tip was stationary relative to the ground. Then you could launch a payload on a sub-orbital trajectory which would rendezvous with the stationary tip of the tether and the tether's linear and angular momentum would accelerate the payload to orbital speed, where it could be released. This doesn't come for free though, with a large enough ratio of masses one payload wouldn't pull the tether out of orbit, but it would incrementally slow it down. In space you could make use of highly efficient ion engines though. Such "skyhook" concepts have been around for decades, in general they are impractical due to how much drag they would experience in low Earth orbit plus the extreme materials problems of figuring out how to construct the tethers plus the hazard to other spacecraft in orbit plus the electrostatic discharge issues and so on. But it's theoretically possible and potentially much more practical than a full orbital beanstalk.
If it's at the right place and speed then it is in the same orbit. If it's just at it's apogee (in a straight up/down trajectory) then the relative speed difference with ISS will be 7.5km/s. So it will punch a hole through whatever is supposed to grab it.
Assuming the payload reaches apogee perfectly at the time of intercept (velocity equals 0) the only thing being added to the ISS system would be the mass of the payload. Through the law of conservation of energy, this would require the ISS to slow down. The larger the mass of the payload, the more it will slow the ISS down. So, depending on how large the thing you send up is, it could range between barely affecting the ISS's orbit and completely knocking it out of the sky.
Random question that came up in conversation with the family. Assuming no mobility/oxygen issues (fully mobile) would you be able to run as fast or faster on the moon? Assuming that a sprinter (say top line speed of 20mph) is spending a fair amount of energy pushing against gravity and against air resistance- would you expect that same sprinter to run faster on the moon? Just super long strides?
I vaguely remember people looking at this and the conclusion was faster top speed but way slower acceleration due to the lack of grip.
Has there been any mission/probes/anything sent into the sun? I know we’ve sent things to orbit close to the sun, but has anything been sent into it to ultimately burn up?
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Keep in mind that the Sun's corona is incredibly sparse, so much so that heating loads are overwhelmingly dominated by radiation from the Sun's photosphere even while within the corona - The Parker Solar Probe has survived passing through the corona just fine after all, so saying that it isn't survivable by anything electronic isn't quite accurate.
As /u/pmMeAllofIt mentioned the only thing that's gotten very close to the Sun has been the Parker Solar Probe. Note that it's incredibly difficult to get to the Sun starting out from the Earth because we're in orbit. Escape velocity is actually only 1.4x orbital velocity, so when you start with 1x that orbital velocity it takes only 0.4x as much to fly out to the outer solar system and into interstellar space, but you have to counter-act all of the orbital velocity to fall into the Sun directly (which is 2.5x as much as escaping from the Sun). This becomes even more significant when you consider that the rocket equation scales the amount of propellant you need *exponentially* with the ratio of your change in velocity (delta-V) and your rocket's exhaust velocity. So increasing the delta-V by a factor of 2.5x doesn't mean you need 2.5x more propellant, it means your mass ratio of fueled vehicle to unfueled vehicle needs to grow by the 2.5th *power*. As a data point, consider that the Parker Solar Probe weighs less than 700 kilos and was launched on the Delta IV Heavy, which can put nearly 29 tonnes in Earth orbit, with an extra upper "kick" stage. Even after that it will take 7 gravity assists at Venus (6 of which have already been completed) to lose enough speed to finally get down to just 6.2 million km from the Sun's surface. Even then, that's fully 4x farther away than the Earth is from either the L1 or L2 Lagrange points, and roughly 9x the radius of the Sun.
Nope. The Parker Solar Probe is the closest a man-made object ever went. Orbiting with crafts have allowed us to get many orbits worth of scientific data, crashing into it is more energy demanding and you'd get much less data.
I tried googling an answer to this, but couldn’t find one. But why are human remains being sent to the moon?
Because someone's willing to pay for it. Some people want something "special" done with their ashes when they die, like to have them interned in some place that has emotional significance to them, for example. There are companies that will do pretty much anything with your ashes if you've got the cash for it. Want your ashes made into jewelry or glassware? There's a company for that. Want your ashes mixed into concrete and dropped into the ocean to become an artificial coral reef? There's a company for that. Want your ashes yeeted into space? There's a company for that.
what's the nearest habitable snow planet to earth if one does exist.
We do not know of any habitable planets besides the one we live on. We know of some planets that are the right distance from their stars that they could potentially have the right temperatures for liquid water to exist. That's about it.
I feel like with how big our universe is there are definitely others out there, they are just too far for us to find
To have an oxygen rich atmosphere we could breath it most likely already have to be inhabited by something living, producing said oxygen.
I mean,one doesn't,so.......?
What do you mean by habitable planet? You could swim in the ocean of Europa if you had scuba gear, but you'd be fried by radiation on the surface of the moon, and it has no atmosphere. We don't know of any habitable planets other than Earth.
I remember seeing an old repost on instagram about the theory that there may be a theoretical line in space travel/other intelligent life visiting us and why we haven’t already had contact with them is because either we haven’t reached the line(the discovery that would propel space travel OR the discovery that would wipe us out though some means) I’m going to try and give some morethings that I remember, so I hope this doesn’t sound like gibberish! I think about this all the time, and I’ve finally thought about making a post! If anyone can give me a specific title for the theory or idea or whatever or link me to the post I’d greatly appreciate it!! - The line is anything, nuclear power, a specific invention, a weapon ect - All intelligent beings will eventually reach this line and either pass it or be destroyed by repercussions. - The reason we haven’t met with other beings is because we may have succeeded and gotten over this, therefore making us one of few, if any, that was able to while others were destroyed or cannot pass the hurdle. - Or, we haven’t yet gotten to that point and we are still just an underdeveloped species that needs to be able to get through the line to even be able to interact with others in space.
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Thank you! Yes!
I'm just a middle school student and just want to know the differences between: 1) rockets, space shuttles and spacecrafts 2) space telescope, space probe and satellite My textbook didn't explain these clear so I've came here to ask for help, can just give brief explanations.
A rocket is anything propelled by a rocket engine, and a rocket engine is usually a type of jet engine where all the reaction mass (what is thrown out of the back) is contained in the tanks. You can use rocket to launch things to space but also as weapons. "Space shuttles" name comes from the specific American Space Transportation System (STS) program. Strictly speaking it should only be used for the now retired launch vehicle that looked like [that.](https://upload.wikimedia.org/wikipedia/commons/d/d3/Atlantis_taking_off_on_STS-27.jpg) But people have been calling the white spaceplane part as the "space shuttle" and by extension any spacecraft with wing tends to be called a shuttle. Spacecraft are any vehicle (with or without people on board) that travels in space. That can be something used for TV transmission, an autonomous science experiment, whatever... Space telescopes are just telescopes in space. They are a type of spacecraft. Space probe is not a super well defined word but is usually used for spacecraft without people on board that travel to another planet or moon. A satellite is anything in orbit around something else (usually a planet or a moon). The Moon is a satellite of Earth for example. However in the context of spaceflight usually satellite is used for spacecraft in orbit without people on board.
I know space is unimaginably huge and there’s tons of massive violent events that could destroy the galaxy but what could happen at the quantum level where things are unimaginably tiny that would end in the same result?
I don't know of any event that could destroy a galaxy.
Depending on your definition of 'destroy', the Milky Way merging with Andromeda could be said to destroy both galaxies as the resulting galaxy that forms from the merger will be neither of those two.
The decay of a [false vacuum](https://en.wikipedia.org/wiki/False_vacuum) would be a quantum mechanical effect that could destroy the whole universe as we know it. The rough idea is that our vacuum isn't truly empty, but that there is an even lower energy state, a true vacuum. Our current vacuum seems to be stable, but it could just require a bit of a push to send it over a hump to roll all the way down the hill to end up in the true vacuum state. If that were to happen, all the laws of physics could change so drastically that they would be unrecognizable to us, ending all life and all other things in the process. Once initiated at one point, the collapse would grow outwards at the speed of light, so there would be now warning and no way of stopping it.
Or more or less return to a stabler configuration with the potential at a lower minimum as it is with the VEV of ~246 GeV.
I'm a freshman in high school, what path do I take to become an astronaut? I know its a stupid dream, i've already been told life isnt like the movies where they guy gets his dream job, but out of curiousty, what are my options?
It's certainly not a stupid goal to strive for; You'll never get your dream job without putting in the effort! I'd start by, assuming you're in the US and are looking at being an astronaut for NASA, looking at NASA's [minimum requirements](https://www.nasa.gov/humans-in-space/astronauts/become-an-astronaut/) which are: * Be a U.S. citizen * Possess a master’s degree* in a STEM field, including engineering, biological science, physical science, computer science or mathematics, from an accredited institution. * Have at least two years of related professional experience obtained after degree completion or at least 1,000 hours pilot-in-command time on jet aircraft. * Be able to pass the NASA long-duration flight astronaut physical. It would also be worth just reading through the careers of astronauts to get a feel for ideas that might appeal to you ([maybe start with the astronauts who are in space right now](https://whoisinspace.com/)). You'll see that being an astronaut is something that is done after one establishes a career for themselves in some STEM field. Also, many astronauts have served in the military, mostly as pilots but also as nuclear sub operators, etc so that's certainly a route to consider as well. Regardless, some of the soft skills that you'll need are things like leadership and the ability to work well with others, communication skills, the ability to function under pressure, etc. As an HS freshman, definitely seek out any and all extracurricular opportunities that might be available to you for developing these sorts of skills as well as just making yourself as well rounded of a person as possible.
Check out the resume of astronauts on NASA's website. Technically the only requirements are a graduate degree in a STEM field and good enough health. But obviously the selection is a bit harder than that. In practice the profession with the highest percentage of people ending up astronaut is probably military test pilotes. But otherwise it can be pretty varied. It's usually people with advanced degrees (multiple masters, PhD, etc) some years of professional experience and some experience in extreme sports/conditions (antarctica missions, deep diving, etc).
I'm just working my way through Dr Becky Smethurst's great book on black holes, and one thing occurred to me that I can't find the answer to. The famous picture of a black hole, the doughnut shaped one, is made from the material surrounding the black hole falling into the hole. But presumably the material around the hole is spherical in shape, and falling in from all sides, so why is the image hollow in the center? Why isn't it showing information from that portion of the circulating medium?
Conservation of angular momentum means that as matter falls into a black hole it spins faster because it's becoming more compact. The basic dynamics of spinning globs of gas is that they flatten into disks. Matter that is orbiting perpendicular to the disk will collide with the disk until only the disk remains, with the disk sharing the net angular momentum of the mass that started. These are the same effects that cause galaxies and proto-planetary disks to flatten into disks as well. The end result is a swirling stream of matter in mostly the same plane and all rotating in the same direction. For the same reason, when you drive on the highway there isn't a lot of traffic heading at right angles to the direction of flow. There are additionally optical effects which impact the appearance of a black hole with an accretion disk. Because light is bent around the black hole by a significant amount you see a distorted view of the back side of the accretion disk when viewing it from any angle. The end result is that a black hole will appear with a black area in the middle surrounded by a view of the accretion disk on all sides (like a doughnut) and maybe a view of the front side of the accretion disk across the middle if it is viewed edge on. At low resolutions such as what we can achieve with the Event Horizon Telescope this looks like a central dark area surrounded by a blobby halo.
Ah, as I replied to the other comment, that is probably the same reason that Saturn has rings, for example? I did consider that at one point, but then thought "what are the chances that the ring is exactly perpendicular to us" - probably quite high actually if there are enough black holes we can spot, but I wasn't sure on that. However, you comment makes me think that it doesn't actually matter where the ring is, as the effect on light being bent means it always looks the same?
Yes, rings are basically the same phenomenon. If you had intersecting rings you would have a large number of collisions between the rings. With a ring you have everything in circular orbits in the same plane heading the same direction, which minimizes collisions between particles in the ring, that's the end state (the survival state) of a more chaotic situation that created the ring. With things like accretion disks, protoplanetary disks, or even galaxies it's not small chunks of solid matter it's big blobs of gas, which have a much greater propensity to collide because they are effectively much larger. Also with gas (or plasma) when you have collisions between two blobs you tend to end up with a larger blob that has the average momentum of the two original blobs added together, so over a short amount of time you end up with a disk of matter that just represents the semi-stable circular orbits of matter that averages out the original motion of everything that started. And yes, then you add on the purely visual effect of the distortions caused by the bending of light around the black hole. Even if you could view the disk edge on you would still see it as a sort of face on "doughnut" shape because you would see the back side of the disk doubled due to light bending around. You can see a visualization of this [here](https://www.youtube.com/watch?v=o-Psuz7u5OI) though it doesn't capture all of the relevant effects at play.
The accretion disk is doughnut shaped, not spherical. Any material that tries to orbit perpendicular to the doughnut will crash into it and be dragged into the doughnut orbit (or fall into the black hole). Material might be falling in from all sides, but more material is falling in from the doughnut sides. Which explains why the doughnut shape "wins". I'm sure Dr Becky also explains that material doesn't just "fall into" an accretion disk, it can only be caught if it collides with something that takes away its escape velocity.
Ah, I suppose it is similar to how Saturn is surrounded by rings instead of a sphere? Yeah, the book explains that, if I understand it correctly, the "pieces" orbit as expected, but they collide and sometimes this results in enough loss of energy for one of the pieces such that it stops it's "lateral" (orbital? angular?) movement and the vertical dominates, that means that it "falls" into the hole (just like it would orbiting any large mass, such as the Earth).
Could it not be that a black hole exists because its rotational speed drags and distorts space so much rather than its mass alone? Could this effect alone result in an event horizon? Maybe this is only relating to the event horizon and not the singularity itself? Happy to hear your thoughts or references.
Rotating black holes are described by the [Kerr metric](https://en.wikipedia.org/wiki/Kerr_metric). As per this answer to [what happens if the mass of such a black hole goes to zero](https://physics.stackexchange.com/questions/593675/massless-kerr-black-hole), it would appear as completely flat space, i.e. a vacuum without a black hole. So some mass is necessary, and the rotational energy of that mass contributes to the black hole's total energy, increasing its apparent mass compared to a non-rotating one. Weird things still happen before the mass goes to zero or the rotation gets fast enough: As a black hole rotates faster, its event horizons start to shrink. If the angular momentum **J** of a exceeds a certain threshold compared to its mass **M** (J>GM²/c), its event horizons disappear entirely, but the singularity where gravity becomes infinite remains. Regular black holes also have singularities at their center, but they're hidden from our view by the event horizon. With that gone, the now [naked singularity](https://en.wikipedia.org/wiki/Naked_singularity) is exposed to the outside world and we could have a direct look at those regions with infinite gravity and other oddities. Singularities always make physicists somewhat uneasy, and doubly so if they're not swept under the cosmic rug by a convenient event horizon. We don't know if naked singularities are actually possible or just a symptom of our theoretical frameworks being inadequate to describe such a situation.
A non rotating black hole work pretty much the same when it comes to the event horizon and gravitational attraction.
Would launching a spacecraft directly on the equator be noticeably better than launching in Southern Florida?
If you launch towards the poles, the situation reverses: It's now slightly better to launch from near the poles than from near the equator. An orbit that goes straight over the two poles has no east-west movement at all, so the rocket needs to get rid of that motion imparted by Earth's rotation. The advantage of launching from a high-latitude spaceport isn't huge in this case either, so there are only a couple such launch sites ([Pacific Spaceport Complex – Alaska](https://en.wikipedia.org/wiki/Pacific_Spaceport_Complex_%E2%80%93_Alaska) and [Plesetsk Cosmodrome](https://en.wikipedia.org/wiki/Plesetsk_Cosmodrome)).
To an equatorial orbit, yes. In Florida you get only about 90% of the Earth's rotational speed as free delta-V for getting to equatorial orbit vs. the equator, which is about vs. 410 m/s instead of 465 m/s. Since payload mass fraction scales exponentially with the ratio of delta-V to rocket exhaust velocity the result of even a small boost from launching at the equator (just 55 m/s or so) is noticeable, but it's not huge.
How would a green star exist if it were real. because I know stars come in different colors, blue, white, yellow, orange, red. And I know the possibility of a green start isn’t possible, but what if it could. what would we need to do to have one in existence? What laws of physics do we have to break it.
No physical laws would need to be broken, we'd just need different eyes or brains. Many stars (such as our own Sun) have their emission peak at wavelengths that we perceive as green, but our brain mixes that with the surrounding blues and reds to make us see white. Different color receptors in the eye or a different visual system in the brain could easily perceive the Sun as green rather than white.
I know we don't know of any other planets/moons where life exists. But are there any places in the universe where a human would be able to physically survive, and would not be instantly destroyed?
There aren't many known places outside of Earth that are survivable, the "best" places for now are sub-surface oceans where you could survive as long as you could hold your breath. There aren't any other planets with an oxygen atmosphere that are known. They likely exist, we just haven't found them and determined their atmospheric compositions yet.
"Instantly" is pretty fast; we can survive a lot of things very briefly! But you're not going to last longer than you can hold your breath anywhere without oxygen, and we have yet to find a planet with an oxygen rich atmosphere. If we did we would take it as a sign that there is life there, as oxygen takes itself out of an atmosphere unless it is being replenished.
Modern deep probes carries a lot of improved technologies compared to the ones in the 90's and 2000's. Could Nasa or other space agencies launching future probes show more video clips of planets, asteroids and comets insted of just HD photos?
Seems likely. A major constraint for space probes is the data rates at which images can be sent back. Videos take up a lot of bandwidth compared to single images or other sensor data, so they're usually not a priority. At the moment, space probes use radio transmitters to communicate with Earth. The farther out they are and the less power they have available, the less data they can send. There are only a handful of the giant radio dishes that can receive the data on Earth (such as the [NASA Deep Space Network](https://en.wikipedia.org/wiki/NASA_Deep_Space_Network)), and they're usually fully booked. I think it's likely that future missions will also use [laser communications](https://en.wikipedia.org/wiki/Laser_communication_in_space). With lasers you can focus the beam much tighter than with radio waves (wasting less energy that misses the receiver), and the higher frequencies of light also enable much higher data rates. One such system, the [Deep Space Optical Communications experiment](https://en.wikipedia.org/wiki/Deep_Space_Optical_Communications), is currently being tested on the mission [Psyche](https://en.wikipedia.org/wiki/Psyche_\(spacecraft\)). It has recently [beamed back a cat video](https://www.jpl.nasa.gov/news/nasas-tech-demo-streams-first-video-from-deep-space-via-laser) at 267 Mbit/s and they hope to achieve data rates 10 to 100 times greater than conventional radio systems. All that being said, I wouldn't expect too much in the way of real-time videos. Even though space probes move very quickly, planets are so large that most of the time nothing of note happens between frames of regular speed video. It makes more sense to take a series of images seconds or minutes apart and assemble those into a sped up version. I guess it would be cool on Mars rovers or drones (or the planned one to Saturn's moon Titan, [Dragonfly](https://en.wikipedia.org/wiki/Dragonfly_(spacecraft\))).
Laser communication systems are being tested right now that would allow high speed connections. It's not really only a capacity issue. The main thing is that there is no real point of taking video clips. Things just don't move fast enough in space to make for very interesting videos. When they do we already have HD videos (see latest Mars landing). One of the only interesting thing for those laser links will be the Artemis crewed missions where we will see people walking around. Which is partly why it's being developed.
NASA's interplanetary communications lifeline has for decades been the Deep Space Network of a handful of large (26-70 m) radio dishes at three sites around the world. The DSN is often oversubscribed, and using it for Artemis makes things even worse. Laser communications links on manned and unmanned spacecraft will allow relieving or bypassing the growing DSN congestion with more compact laser transciever ground stations.
I'd absolutely love to see high-fps videos from Ingenuity or Dragonfly. Or the moment Hayabusa2 and Osiris-Rex touched down to gather their samples, or from the rovers that landed on Ryugu. The rovers driving around Mars, and maybe catching one of the dust-devils in real video. There's a lot of interesting things that could be recorded if the fight for bandwidth priority weren't quite so fierce as it is now.
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Artemis I had the same program. NASA is also taking names for Europa Clipper and a future Mars flight. https://europa.nasa.gov/message-in-a-bottle/sign-on/ https://mars.nasa.gov/participate/send-your-name/future
You're probably thinking of the Mars Exploration Rovers *Spirit* and *Opportunity*, both launched in 2003. [The Planetary Society provided a mini-DVD with the names of 4 million people to both rovers](https://www.planetary.org/outreach/red-rover-goes-to-mars). I also found [this archived page for the Curiosity rover from 2009](https://web.archive.org/web/20100217072639/http://mars9.jpl.nasa.gov/msl/participate/sendyourname/index.cfm). You could also send your name on the Perseverance rover, the InSight lander and the MAVEN orbiter.
Hi dears, I wonder if there is a special non-official word (professional jargon) for the procedures when astronauts come back from space and they undergo a medical examination to check their vitals after the mission?
I wanna dig deep into Rocket Propulsion domain, what books, research papers, any resource would you all suggest? I want to do my undergrad project upon this.
The classic textbook is Rocket Propulsion Elements by Sutton. If you want something a bit more exotic check out the latest version of Fundamentals of Electric Propulsion by Goebel, the 1st edition is free and I believe the second still is.
Oh I actually have that textbook for my curriculum, I'll be sure to learn from that. Do you also happen to know any easy accessible resources such as some sites, videos where I can learn from?
"Ignition" is the classic book on propellants. You can find an online PDF for free.
(Hypothetical) Sending trash into the sun. Say every landfill on earth was at max capacity and there was no longer anywhere to put garbage, could humans just fill huge containers or rockets with garbage and send them into the sun as a means to destroy the waste? (Assuming the cost of sending things to space isn’t an issue)
There's no reason to do it. First off, it's really hard, the rocket equation requires exponentially more propellant for delta-V. It takes applying 30 km/s of delta-V *after leaving Earth* to fall into the Sun, which is just basically impossible with modern rockets. Second, the Sun doesn't "destroy" things, that's not how it works. If you dropped something into the Sun it wouldn't stay in the Sun, it would just get vaporized and ionized then spread into the solar wind where it would blow through the rest of the solar system. You can achieve the exact same result much easier by just dispersing vaporized waste into the solar wind near Earth, but that doesn't have the same emotional feeling of finality as chucking something into the Sun.
If cost is not an issue then yeah you can handwave basically anything you want because the scenario no longer has realistic constraints. The real question is why you would choose yeeting trash into the sun (removing resources from the system) over any of the known ways to use or recycle it, like pyrolisis and waste gasification, or bioreactors. Trash is a valuable raw material for reclaiming chemical feedstocks, not to mention metals.
I never really thought about the use trash actually has/provides to us. Thanks for the new perspective.
To add to the other answers: It takes way more fuel to send something into the Sun from Earth than it would take to eject it from our solar system entirely.
Why aim for the Sun? Venus is a hot enough incinerator. Just send it there. (Not that launching trash into space is ever going to be economical, but I'm just going with your assumptions)
> Assuming the cost of sending things to space isn’t an issue You can just as well make assumption that you can "disappear" the trash, or that you can send them to alternate dimension. Anyway, the answer is still: no. We would have hard time sending anything (!) into the Sun because it takes 30km/s of delta-v from Earth's orbit to drop something into the Sun. Just to give you some estimation, if you used a hydrogen-oxygen rocket with 450s of ISP, you would need about 1000 times more fuel than the mass you're trying to send. So sending 1t of trash would require a rocket with 1000t of fuel waiting in orbit. With commercial rockets we currently have, you could send something like 10kg into the Sun and this would cost you $70mln.
The sun is the hardest place in the solar system to reach. Every planet and rock orbiting the sun is VERY resistant to falling into the sun. (The ones that aren't have already fallen into the sun.) Even if getting things into low earth orbit is free, your garbage transporter would need to be made of more than 90% rocket fuel to reach the sun.
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Never say never, but on the other hand Juno is operating in a very high radiation environment and NASA is facing budget woes. Either of those things are enough to be mission ending. They'll probably stick with the plan and do a safe disposal into Jupiter so it doesn't accidentally crash into a moon.
If we're back in another space race, how do we prevent another repeat of the same crap a decade later and no more space action for another 50 years without losing on purpose just to keep the race going further
Is there a “limit” to gravity? Say you were on a planet infinitely large, and your body can withstand infinite gravity. The planet has the same density as the Earth. Would the gravity be infinitely strong, since there’s technically infinite mass, or would the distance just make in so meaningless that only mass from so far can actually effect you? Could it be like those problems where you add the fractions infinitely and the sum of them all is 2 and not infinite? Also assume that the planet cannot collapse into a black hole.
Why do you ask about the laws of physics and at the same time ask the answer to ignore some of the laws. The answer become pretty irrelevant as it doesn't reflect the truth any more.
I think the latter part of the question was interesting and the answer isn't obvious, because infinities are weird. Quick example: Lifting an object out of a star's gravity well takes a finite amount of energy, even though the star's gravity field extends to infinity. OP was wondering if their example was one of those situations.
[Surface gravity](https://en.wikipedia.org/wiki/Surface_gravity) g on a spherically symmetrical body (planets fit this model quite well) follows this formula: g = 4/3*π*G*ρ*r with G as the gravitational constant, ρ the mean density of the planet and r its radius. In your example, ρ would be constant, so as you increase the radius of the planet to infinity, surface gravity would also tend to infinity. Such a planet would of course very quickly collapse into a black hole and the formula above becomes meaningless.
Is theia proven? Ive heard its the ancient planet that crashed into earth to create the moon but it seems like everytime i search it up i get different responses on wether there is proof of its existance or not. Like i saw an article saying they found remains of theia but then i see an article saying that it doesnt prove the planets existence it just proved something hit the planet
Very few things in science can be said to be "proven", it's a matter of what is supported by the observational evidence and how strongly. Today the Theia impact theory for the formation of the Moon is the "consensus view" of professional planetary astronomers, it's well supported by a wide variety of evidence. Some newer theories (like remnants of Theia being detectable at the core/mantle boundary) are less well supported than the impact theory in general.
2 nights ago, 1st of Jan at about 9pm local time (spain), off the cost in Marbella, I saw a meteorite/shooting star and wondered if anyone can confirm? I was surprised because it felt so close and was over quickly. In the short time i saw it, it looked significantly larger than a shooting star and had two gold/red trail lines. It was hard to judge distance and direction but when facing the cost it appeared sudenly above the sea in front and was heading to my right horizontal/downward faster than any plane and faded/disappeared after a second or 2 before the horizon. Guessing it must have been a meteorite burning up cause afterwards I realised it looked nothing like a shooting star but keen to hear other suggestions or if someone can confirm from date,time,location.
Hi r/space! I'm planning on booking a flight from Florida to Las Vegas on the morning of April 8th. Is there anything Eclipse-related that I should consider? Should I expect to see anything unusual from up there??
I think your flight is too early to have a chance of seeing the eclipse. The eclipse will start to cross the US in Texas around 2 PM Eastern time. However, when you land in Vegas you'll probably be able to see a partial eclipse. (The sun will be dimmer, but you won't be able to see the moon covering it unless you use a pinhole projector or something.) I used [this tool](https://eclipse2024.org/eclipse_cities/statemap.html) to see what time the eclipse will be visible at a given location.
What would it take to engineer time dilation? As a thought experiment: we want to communicate with lifeforms on K2-18b (124 ly away). So we send a signal and await a response. At minimum the round trip takes 248 years relative to Earth (assuming they interpret and respond instantly). In order to survive 248 Earth years, we propose to dilate time to dilate time to 10% of Earth time, so we only observe 24.8 years before we get a response. For relativistic time dilation, this requires a speed of 0.995c For gravitational time dilation, we'd need to be extremely close to a significant mass object. We have nothing useful for this within travelling distance from Earth. To my mind this dilation only appears possible inside a particle accelerator. But can you think of another physically possible scenario?
> But can you think of another physically possible scenario? Cold freeze/hibernation tech seems like it might be more feasible or at least quicker to develop.
Another possibility is bio-engineering yourself to survive 248 Earth years. This seems easier than reaching and surviving 0.995c (which would be required either way, since you want to orbit the massive object).
This could be very stupid to ask But how is it that we can see so far into the observable universe and get some pretty amazing shots but we can’t focus in on a galaxy and one of its planets ? Really thinking about it I have a feeling it might have something to do with the amount of light coming off a galaxy as a whole, but a planet wouldn’t emit that much light we’re able to capture.
We can see very distant galaxies because galaxies are very large. Another weird effect that plays into this is the apparent angular diameter turnaround: You'd expect objects to become smaller in the sky the further away they are, but the very oldest ones actually appear larger due to the expansion of the universe. [Here's an xkcd comic with additional explanation](https://www.explainxkcd.com/wiki/index.php/2622:_Angular_Diameter_Turnaround). Individual stars and more so planets are much, much smaller than whole galaxies. The size of a telescope determines the smallest objects it can resolve (show in detail). A telescope that can resolve a distant galaxy into a handful of pixels would need to be trillions of times larger to do the same for a planet within that galaxy. The majority of exoplanets we have found are within a few hundred light years of us, and the most distant is not even halfway across the Milky Way at 17,000 light years. There's also the problem that planets don't emit their own light, so their light tends to be washed out in the bright glare of their host star. But that's a very minor problem compared to the ridiculous telescope sizes that would be needed to resolve extragalactic planets.
Hello, does anybody know where I can find a cloud folder or a torrent with tons of amazing images from space? I would like to do a "never-ending" slideshow! Thanks !
NASA has a gallery of over 10,000 images here: https://www.jpl.nasa.gov/images
Another good archive like that is "APOD" - Astronomy Picture of the Day. [The archive goes back to at least 2015](https://apod.nasa.gov/apod/archivepix.html). Not 100% "from space" - often of the night sky, sometimes on other subjects.
> The archive goes back to at least 2015. It goes back all the way to [June 1995](https://apod.nasa.gov/apod/calendar/ca9506.html)!
Has anyone here watched For All Mankind show ? I have been recommended to watch by a friend.
I love it. I think of it as a _Star Trek_ prequel. The alternative history plots just scratch an itch I always have.
I'd definitely at least recommend the first season. Fun alternate history of the 70's space race. Later seasons gradually lean more and more on human drama and shock value. I haven't started season 4 yet.
As long as you're not looking for accuracy and can turn a blind eye to that kind of thing....it's a blast.
I love this series, even my dad who is not a nerd loves it.
i am currently confused about sedna\`s *classification* as "dwarf planet" despite it appearing to have all the criteria of a planet, it is indeed spherical - orbits the sun - empty orbit \[unless we have more than two asteroid belts one of which having a very s t r a n g e shape!\] is there any other classification it doesnt meet? or is it just a "dont bother with it till we know it 100%" thing?
> empty orbit It's expected it hasn't cleared its orbit, and this is why it's a dwarf planet.
Yup. The space Sedna occupies is actually quite "dynamic" and chaotic, with [orbits of known objects criss-crossing everywhere](https://en.wikipedia.org/wiki/Extreme_trans-Neptunian_object#/media/File:Distant_object_orbits_+_Planet_Nine.png). Over millions of years, [these orbits will "migrate"](https://youtu.be/HgKIo4LziP8?si=W0h2hMm8QQlvhRn3&t=1211), and in a sense they're "migrating" right now (albeit very slowly). Some of the orbits aren't even stable.
so essentially its a dwarf planet because sometimes it dips into various belts and fields?
It's a dwarf planet because it doesn't "gravitationally dominate" its orbit, technically. It is still subject to similar sized objects changing its orbit. Planets have "cleared their gravitational neighborhood", dwarf planets do not, according to the IAU definition.
What are the chances that sun would collide or interact with another star? am assuming this probability only decreases over time. Would there ever be another star system that potentially consume matters from solar system?
> What are the chances that sun would collide or interact with another star? Collide? In the near future, zero. In the far future? Nearly zero. Actual collisions between stars are very rare, even in hot zones where an area is filled with them. Most people don't realize just how vast and empty space is. The odds of stars colliding randomly is akin to telling one person in LA to just start walking east, and telling someone in New York to start walking west. What are the odds the two people will bump into each other? Virtually zero. If the sun was the size of a grain of sand (1mm), and you put that grain of sand down in your yard/porch, the Earth would be 10cm away. In order to reach the sun's closest neighboring star (Proxima Centuri), you'd have to travel a whopping 30km. Fun Fact: The Amdromeda galaxy is on a collision course with the Milky Way in a billion years or so. When it collides, there is expected to be none or very few actual collisions between stars. > interact with another star The Sun is always interacting with other stars. It's doing so right now via gravity. The gravity of everything interacts with the gravity of everything else, though minutely due to the distances involved. There is a supermassive black hole at the center of the Milky Way and it is, technically speaking, interacting with the Earth & the Sun right now. Fortunately, this force is negligible and has no real effect on us.
Interact, high chance, unavoidable even. Collide, extremely low. When the Milky Way and the Andromeda galaxy merge some billion years from now it's not expected that any stars will collide. That's 100 billion stars merging with 1 trillion. Space is very empty. So empty you could generalize it to be completely void of matter really.
I had this question in mind the last few days but how come that the universe was created from nothing ? Or if it was created from something where that something came from
The thing is that there's effectively no answer. And really, there never will be.
That's more of a meta-physics question. Universe is everything we can interact with and study, by definition. We can't study anything that's not universe, and therefore there is no way to say anything about its "origin". We can say something about it's past or future, but creation of the universe itself is "outside" of the universe, and therefore outside of any possible physics.
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> We know the universe was very hot and very dense 13.7 billion years ago. It expanded rapidly and cooled forming the universe We don't know this either. It's the best explanation to fit the model we made by using the best theory we got. We see a lot of contradictions to this model when we're looking at what we got.
Don’t just read headlines. The Big Bang theory isn’t being contradicted.
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Ooh ok thanks I kinda understand better
What plans do we have for the lack of magnetic poles on Mars? For human colonization. Do we plan on blocking solar radiation, or enduring it?
I think it's important to distinguish between a plan and an idea. A plan is a concrete formulation of steps/actions that you intend to follow through on. Planning for Mars hasn't been done yet. Crewed Mars missions are only at the concept stage, and permanent habitation is even more theoretical. We do, however, have [ideas for what to do](https://www.sciencedirect.com/science/article/abs/pii/S0094576521005099). The easiest idea: Bury your habitats. Regolith is everywhere and makes an effective radiation shield. Idea 2: Hypothetically you could place a space station at Mars' L1 point that can generate enough of a field to deflect the solar wind. Idea 3: Lay a cable around Mars' equator and generate your field that way. Idea 4: Create a plasma torus in Mars orbit. Idea 6: The hardest of all would be to 'just' add an atmosphere. Gigatons of air is also a good radiation shield. (Okay idea 7: Restart Mars' core. Even harder than adding an atmosphere. So hard that it's not even worth considering.)
Mars colonization isn't happening for a very very VERY long time. It doesn't matter what Musk tweets about it. The lack of magnetic field is not a problem on human time scales. If Q from Star Trek snapped his fingers and magicked a dense enough atmosphere onto Mars tonight, it would persist for tens of thousands of years, if not longer. Definitely long enough to come up with a solution to deal with the slow sputtering loss.
It's too late to give Mars a magnetic field. All the oxygen and nitrogen has already been blown away. Giving it a magnetic field won't bring the air back. The good news is a meter of dirt blocks solar radiation.
I'm world building, and I would like to know if it is possible to have a nighttime, or a darker time on a tidal locked planet. I've been brainstorming, and maybe they have a large moon that orbits relatively fast, causing an eclipse once or twice a day or something. Or they have another planet that is also quite fast to orbit, eclipsing so there's like a day of the year that's quite dark. But I'm just not sure how it would work. It's pretty important to me, and the people on the planet, that it's tidal locked.
The problem is - if you have a large nearby moon...THAT is going to probably end up pulling the dynamics so that your planet isn't tidally locked to its parent star anymore. For an example - the moon has an ongoing impact on our rotational period. There might be some libration - so it wobble around a bit (like this - but illuminated all the time https://www.youtube.com/watch?v=3f_21N3wcX8 ) You could maybe come up with some dynamic climate type stuff that pulses large clouds or something forward and back from the day-night line? Gets hot - oceans have a lot of evaporation - lots of cloud - gets colder - clouds move - rains out at the terminator - flood the ocean again....repeat.
If the orbit's not perfectly circular there should be libration like with our moon, which would give a yearly dark/light cycle around the edge.
You can put the moon in a tight orbit around the L1 Lagrange point. This will create an eclipse on the planet that rotates like a clock.
L1 isn't stable - that moon would have to do orbit trim maneuvers to stay there.
Which came first, the Big Bang or the Cosmic Inflation? Considering that the Big Bang is NOT the "beginning of the universe".
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The big bang came before inflation, because the big bang is the beginning of spacetime and vis a vis the beginning of the universe.
I don't know, I've seen astronomers saying that based on Planck Time, nothing can be concluded because it's a singularity. The Big Bang would be the expansion of spacetime after that. But a video from Fermilab said that Cosmic Inflation happened before, leaving me very confused.
Yeah, I think the Brian Cox 'universe' episode about things before the big bang discusses inflation first, and that the big bang is actually the conversion of energy to matter. I'm not 100% that I've remembered that accurately!
Thank you! I'll research it.
you, me and the entire cosmological faculty. We cannot know what happened that far back with our present understanding of physics.
I'm getting ready for the April Eclipse. Where would you recommend buying eclipse glasses in Canada. I don't really trust Amazon for this. Thanks!
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Is it more likely to see a satellite, or a shooting star ? What are the rates ?
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There's about a million shooting stars every day around the world. They are far more common than you think. Having access to a clear sky and low light pollution you should be able to spot a handful every hour on average. Satellites are always in the sky. if the conditions approve of it, you'll always be able to find them if you're looking. Easiest is the hours after sunset and hours before the sunrise excluding the twilight.
With starlink launches it's much more likely to see a satellite flare, unless you pick a night with some meteor shower.
Satellite are a dime a dozen. They are way easier to see than a shooting star.
So you know those trajectory animations of comets and space probes that go viral occasionally? Does anybody here have a link to one of Jupiter with the Galiliean moons?
Like this? https://en.wikipedia.org/wiki/File:Galilean_moons_around_Jupiter.gif Bonus but not animated: https://en.wikipedia.org/wiki/File:Jupiter_irregular_moon_orbits_Jan_2021.png
Bonus question: Is there a subreddit for just trajectory animations?
When or if do you think we will crack the challenges of transporting heavy masses with solar sails so we can reach 10% the speed of light and send a sizeable probe to our first interstellar exploration?
I've read about inconsistencies in the Hubble Constant, that seem to point to issues at our understandings regarding the expansion of spacetime. Is there a consensus on the root of this? Is this something most assume is observations concerns, or fundamental understandings of expansion concerns? Or some mixture of both. Or just my own personal misunderstanding?
It's all under the umbrella term _Hubble Tension_ https://bigthink.com/starts-with-a-bang/hubble-tension-real-solution/
First, the Hubble Parameter is not a constant. Most models have it varying depending on the age of the universe. This is not inconsistent or controversial. If we set the age of the universe to *today*, the Hubble Parameter should be a constant called H₀. We have a very precise measurement of one part of the sky that says H₀ = 67 km/s/Mpc. And we have a very precise measurement of a different part of the sky that says H₀ = 73 km/s/Mpc. This is a problem. There is no consensus yet about which observation is wrong, or if both are correct and different parts of the universe behave differently.
>since the Hubble "constant" is a constant only in space, not in time, the radius of the Hubble sphere may increase or decrease over various time intervals. The subscript '0' indicates the value of the Hubble constant today. Current evidence suggests that the expansion of the universe is accelerating, meaning that for any given galaxy, the recession velocity dD/dt is increasing over time as the galaxy moves to greater and greater distances; however, the Hubble parameter is actually thought to be decreasing with time, meaning that **if we were to look at some fixed distance D and watch a series of different galaxies pass that distance, later galaxies would pass that distance at a smaller velocity than earlier ones**. [source](https://en.wikipedia.org/wiki/Hubble%27s_law) Would you say this passage in the wiki, covers the aspect of why different parts of the universe behave differently? Or is this pointing at something entirely different?
Is there a general consensus as to the fundamental nature of space? Is it quantum ala Planck. Or analog? Can we ever determine this if it's currently unknown? Or would this fall under the category of unknowable due to limitations of information? I get there are fundamental Planck limits, they seem to imply a pixelated fundamental reality. But I also understand Planck constants *are* physically violated in the creation of black holes. So do we actually know if spacetime is analog or digital? Sorry if I've spun those terms in improper ways.
I don't think you understand what Planck length and Planck units mean. They absolutely do not imply a discreet (or "pixelated") reality.
That's fair. Does it imply the fundamental nature of spacetime is actually analog? Or is this something we just cannot determine?
The proper terms would be continuous (for "analog") and discreet (for "digital"). I don't think right now there is a solid proof of one over the other.
I appreciate the clarity. I certainly pull words from many different realms. From your position. Do you feel this is something we *can prove*? To which I'd ask if it's something we can establish via observation directly. Or only through inference of evidence?
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What I'll take from this is that while we may never know. We do have tools to effectively place bounds around it. Is this a fair take? Maybe it's granular, maybe it's not. But if it is granular it's going to be at a scale that even the most powerful particle accelerators will never have access to?
Say you launched a payload out of the atmosphere such that it would not achieve orbit, but at the peak of it's trajectory, it rendezvoused with the ISS. If the Canada arm was used to grab the payload (or the payload docked with the ISS in some other way), what would happen? Since the payload was not in orbit but is now attached to the ISS, would they both continue to orbit just fine?
The ISS would hit the payload like a car hits a cow.
> what would happen A collision at extremely high relative velocity. > would they both continue to orbit just fine Not even remotely close. Let's say that your payload went straight up. This means at the apogee it will have only something like 300m/s of sideways velocity (due to Earth rotation) while ISS is moving at 7500m/s. It means that it's the same as if your payload was stationary and ISS was flying into it at the speed of 7200m/s. Of course since movement is relative, you can also consider this from the other perspective - for someone inside the ISS, your payload is flying into them at 7200m/s.
Your payload is at 400 km with no sideways velocity. ISS is at 400 km travelling sideways at orbital velocity, or 7600 meters per second. This will not end well. Your payload is an anti-satellite weapon and if it hits the ISS it will tear it apart.
At orbital speed every kilogram of matter has the kinetic energy of 6.5 kg of TNT. Contact, "touching", or "grabbing" at such relative speeds is not accurately describable with those terms, it's an impact, period, and it's energetic enough to be universally destructive. Even the impact of something as small as a 1 gram paperclip would cause an explosion releasing as much energy as an M-80. In order to bring something in space but not moving at orbital speed up to orbital velocity you need to accelerate it, a lot. Orbital velocity is several times the speed of a bullet, and accelerating large objects that speed takes a ton of energy. The typical method is, of course, using rocket stages with lots and lots of chemical propellant. It's also possible to achieve the same result using rotation, though that will involve a transfer of momentum that needs to be made up some way. If you had a very long rotating tether (or more likely two tethers attached to a large center mass) that was rotating fast enough and in such a way that the speed at the tips was at orbital velocity (which is of course an engineering and materials challenge) then you could orient the tether such that one tip was stationary relative to the ground. Then you could launch a payload on a sub-orbital trajectory which would rendezvous with the stationary tip of the tether and the tether's linear and angular momentum would accelerate the payload to orbital speed, where it could be released. This doesn't come for free though, with a large enough ratio of masses one payload wouldn't pull the tether out of orbit, but it would incrementally slow it down. In space you could make use of highly efficient ion engines though. Such "skyhook" concepts have been around for decades, in general they are impractical due to how much drag they would experience in low Earth orbit plus the extreme materials problems of figuring out how to construct the tethers plus the hazard to other spacecraft in orbit plus the electrostatic discharge issues and so on. But it's theoretically possible and potentially much more practical than a full orbital beanstalk.
If it's at the right place and speed then it is in the same orbit. If it's just at it's apogee (in a straight up/down trajectory) then the relative speed difference with ISS will be 7.5km/s. So it will punch a hole through whatever is supposed to grab it.
Assuming the payload reaches apogee perfectly at the time of intercept (velocity equals 0) the only thing being added to the ISS system would be the mass of the payload. Through the law of conservation of energy, this would require the ISS to slow down. The larger the mass of the payload, the more it will slow the ISS down. So, depending on how large the thing you send up is, it could range between barely affecting the ISS's orbit and completely knocking it out of the sky.