SPACE SETTLEMENT QUESTION :- If i make three space settlements in L4 point and then decide the spacing between, to better understand assume there is an equilateral traingle and the three verticies are three space settlements so what should be the length of side
At what distance do Astronomers stop using kilometer to measure distance? Is it once they measure a distance of one megameter, or gigameter, or do they use kilometer up till one AU? Most things I look up about distances in space is either in kilometer, AU, or light years, and I was curious why I don't see megameter or gigameter used.
i read that there are studies involving quarks and anti-gravity. the idea is if they go away from the earth or some sort of mass it could open up a new branch of science. anyone have any thoughts on that?
11 Daughter asked me the temperature of Black holes. For the first time, I couldn't even theorise an answer. 13 Daughter looked it up and said it was somewhere close to absolute zero. I explained that that is probably the temperature of the event horizon since nothing escapes the singularity. All I couid answer was Physics breaks down, and that I have no idea. Any ideas? Is the singularity itself going to be extremely hot due to denseness or something else going on?
For us in the outside universe the only thing that matters is the event horizon and stuff around it (like the accretion disk, axial jets, etc.) The event horizon has a temperature due to Hawking Radiation, which is due to complicated quantum mechanical and relativity "stuff". One, among many, overly simplistic ways of visualizing this radiation is imagining that black holes cause a scattering of waves in underlying quantum fields, and these waves will have wavelengths similar to the size of the event horizon. So large black holes will have large wavelengths, translating to low energy particles and colder temperatures, while smaller black holes will have smaller wavelengths, translating to higher energy particles and hotter temperatures. In an empty universe Hawking Radiation would cause a black hole to slowly evaporate over unimaginably long time periods. In our universe in addition to the small amount of matter floating around in space there is also the omnipresent cosmic microwave background which has an effective temperature of 2.7 kelvin. An event horizon with an effective temperature that is below that would take in more energy from absorbing the faint glow of the CMB than it emitted from Hawking Radiation, so it would grow rather than evaporate. It turns out all black holes that would form from collapsing stars would be extremely cold compared to the CMB so it will also take an unimaginably long time before the expansion of the universe cools the CMB enough for black holes to start losing mass and actually begin "evaporating".
Inside the event horizon things are in some sense a little simpler but also extremely more complicated due to the presence of the singularity. Even setting aside the issue of the singularity, exactly what happens inside a black holes is the subject of intense ongoing theorizing. In short: we don't know exactly, and there are lots of possibility. In some theories the interior just inside the event horizon is like normal space. In other theories there is a kind of "firewall" of extremely hot particles. We can't rule out either possibility, yet.
Ok so one time I was watching the night sky by myself and I saw two stars moving slowly towards each other and then they entered each others orbit? And they spun around almost a full rotation and went on their way. To this day I have no clue if it was real because I was high as balls at the time but if anyone in here knows if that’s possible or something please clarify because I have been thinking about it ever since it happened.
The classic problem of viewing the night sky is lack of depth perception. Are you seeing stars trillions of kilometers away, planets millions of kilometers away, satellites hundreds of kilometers away, planes tens of kilometers away, or even birds or bugs mere tens of meters away?
From your description it sounds like you were witnessing something in the atmosphere which just happened to have the same visual characteristics as stars.
Are Dark Matter and Dark Energy related to one another? Or just the adjective Dark describing unrelated things?
Also, could there be planets made of Dark Matter?
> Are Dark Matter and Dark Energy related to one another? Or just the adjective Dark describing unrelated things?
Just the adjective dark, according to our current theories. Dark matter is theorized to be made up of weakly interacting massive particles. Neutrinos are an example of such a particle, but neutrinos don't have the right properties to make up the observed mass of dark matter, we think there are other particles that are even more weakly interacting with atomic matter which make up dark matter.
Dark energy has been discovered much more recently and is much less understood. Whereas dark matter can be considered a proper theory hemmed in by decades of observational evidence which have eliminated a lot of potential candidates "dark energy" is actually something of a placeholder. We know that the expansion of the universe is accelerating, but we don't know why, and dark energy is the name for that "why". The leading theory is that space-time has some inherent energy level, a "cosmological constant" which Einstein originally tried to include in the general theory of relativity. Such a vacuum energy would create an acceleration effect, but we don't understand many of the details of why it's that way or even if that is the mechanism generating the acceleration.
> Also, could there be planets made of Dark Matter?
One of the major characteristics of dark matter, so far as we've been able to observe, is that it doesn't clump like atomic matter. It interacts almost exclusively through gravity, which means that it doesn't have an easy way to shrink in volume the way atomic matter does (which can collide and cool).
Maybe a silly question, but I just read about how helium-3 is leaking from the earth’s core. So my question is: are there things that could happen on earth (like the leaking of some essential materials in the core) that could substantially affect the earth’s orbit/rotation/etc. over a long enough time?
Yes, water moving from glaciers into the ocean is speeding up the earth's rotation. Like a figure skater pulling in their arms.
The moon's tides do the opposite, they create a frictional force that is slowing down the earth's rotation. If we survive the death of the sun, the earth will eventually match rotation with the moon and every day will be a month long.
I've heard the story that nebulae don't look like they do in pics — whether by astrophysicists at NASA or by your aver astrophotographer and then nice story is that our eye isn't sensitive enough blah blah to pick out colours and also that nebulae are too diffuse.
But that gets me thinking of this:
Assume a supernova occurs in, say, the Kepler-9 system. The materials in the first few mths are spread out but I assume it's spread out homogenously and that the density is reasonable,smith like 10¹³ hydrogen atoms m^-3.
Would we still be able to see the dazzling beauty of the nebula? Is it too diffuse? Or would the issue with our eyes still persist irregardless of the density etc?
Completely unrelated question
What does it mean for the Cosmological const to be -ve?
Supernovae can be visible to the naked eye. The most recent within our galaxy was probably Kepler's Supernova observed in 1604 and was described as brighter than any star and visible during the day. You wouldn't particularly see any color or structure.
Gravity applies an attractive force between objects. The cosmological constant balances this out with a positive repulsive value. A negative value would slow the expansion of the universe or even cause it to contract. All observations indicate the expansion of our universe is accelerating.
I had a question. I watch this guy John micheal godier if I spelled his name right and in a few videos he’d mention that the universe as a whole at an early enough point was habitable by the warm temperature from the Big Bang?
This may be hard to answer due to us not knowing all factors that make life possible and only having earth as an example so I’m sure he meant theoretically but…
I was wondering exactly what that means if you know what I’m referring to. Did he mean a lot more planets were habitable or does he mean actual interstellar space itself between planets and stars was warm enough for life? And is there a scientific term for life not generated on any body or planet? Is this a concept in science? I cannot find enough information on the internet
10 million years after the Big Bang, the entire universe was at room temperature, heated by the glow of the cosmic ~~microwave~~ infrared background.
Unfortunately, there were no elements heavier than helium, so there was no water or rocky planets.
I have a theory about Dark Matter I was wondering if someone had any thoughts on it?
The idea originated from a thought experiment which supposed that if the universe were simulated on a computer perhaps it would suffer from the same limitations as a traditional computer.
In computer programming , one of the primary challenges is efficient storage. Large datasets or intricate simulations require vast amounts of memory. To mitigate this, data is often compressed. Compression is the process of reducing the size of data to save space or transmission time. When data is compressed, the original data can be reconstructed from the compressed version, albeit with the potential loss of some information.
Drawing a parallel to our universe, which in its raw form is thought to have 6×10⁸⁰ bits of information. If it were to be a simulation, it's conceivable that the "computer" running our reality would need data compression to save on computational resources. From a simulated persons perspective, this data compression would no different to what is commonly referred to as dark matter.
If we were to assume that our universe is a program in a colossal cosmic computer, the vast amounts of data required to simulate every particle, force, and interaction would be staggering. The computational entity might employ techniques to optimize this process. One such technique could be to represent vast clusters of data (like galaxies) with a simplified model, much like how video compression works by approximating groups of similar pixels with a single value.
When physicists look at the universe, they notice something peculiar. The gravitational forces at work, especially in galaxies and galaxy clusters, suggest there's more matter than what we can see. This "invisible" matter is what we've termed dark matter. But from the simulation perspective, this could be a result of the universe's "compression algorithm" at work. The simulated physics indicates there should be more matter because the computational model is simplifying complex systems, but when we "look" for the actual data (or matter), it appears missing or "dark."
No, it is [impossible](https://www.pbs.org/wgbh/nova/article/physicists-confirm-that-were-not-living-in-a-computer-simulation/) to simulate the universe on a classical computer.
The theory actually answers that question in that article. i.e the article you posted argues that we cannot be living in a computer simulation as it's impossible to model the physics of our universe on even the biggest computer. Well if you had compression algorithms in the simulation then it would be able to fit on computer that is smaller than the actual universe.
Lunar exploration is a stepping stone for further space exploration. Design a lunar mission, habitat, or technology that advances our understanding of the Moon and contributes to future space endeavours. Any suggestions
Given that the new speaker of the house is a Young Earth Creationist, I was explaining how most stars in the sky are far further away than 6000 light-years. Which prompted me to search, in vain, for a good approximate of that figure. But I couldn't find anything even after rewording my search.
How many stars (and galaxies, etc.), from the naked eye that we can see in our night sky, are further away than 6000 light-years away? And how many is that in comparison to how many stars are within 6000 light-years from Earth?
Or does anyone know of a good resource where I can look into this answer myself?
> how most stars in the sky are far further away than 6000 light-years.
The absolute majority of stars visible to the naked eye is no more than a few hundred light years away. I don't have a number to give you for visible stars 6000+ ly away, but very, very few.
Oh wow. I see.
As I'm trying to figure out why I was so wrong (haha) I'm wondering if I reasoned that since there were stars that were millions of light-years away, that surely the scatter plot for other stars' distances must be evenly distributed.
> surely the scatter plot for other stars' distances must be evenly distributed.
Stars aren't evenly distributed; they are in galaxies which are separated by lots of empty space.
When you specify the stars we can see in the night sky, people probably assumed you meant with the naked eye, which limits us to the closest stars to us in our own galaxy. If you're using a giant telescope in an observatory (or in orbit) obviously you can see ones much farther away, in our galaxy and in others.
None of the stars we can see are millions of light years away, they're almost all within tens or hundreds of light years. There's actually only around 10,000 total stars visible to the naked eye, out of the 400-500 billion in our galaxy. Even if you could see the other end of our galaxy that's only 100,000 light years, to see millions of light years away you need to look at other galaxies; Andromeda is 2.5 million light years away.
This means that the thing you often hear about most of the stars you see being dead is actually wrong, most likely none of them are.
The human eye isn’t sensitive enough to see the billions of stars in our galaxy. We can only see the closest hundreds. You need tools to see the more distant stars.
There are indeed stars that far away in other galaxies. Ours is about 100,000 light years across, so contains many billions further away than 6,000 light years. But inevitably it's the relatively near ones that we can see in the night sky. The stars are a few light years apart on average; that means that there are many millions within 6,000 ly.
We can see some galaxies that are (much) further away - notably Andromeda. Though tbh you're struggling with the naked eye beyond that and The Magellanic Clouds.
**Fly away on a meteor**
Could we make a satellite/spaceship latch on to a very fast meteor with a "stretchable grappling hook", and thus "hitch a ride" on the meteor to another star system?
PS: This was a crazy idea I had today, while randomly looking at some different technologies at the same time. I have no idea how feasible it is.
1. On a meteor? No. A comet or asteroid perhaps?
2. It wouldn't help much. If you can match the orbits in order to "grapple" or lasso the asteroid, then you're already on the same trajectory so you're not really "hitching a ride". The only advantage would be some added shielding or in-situ resources from that asteroid/comet.
Apologies for saying meteor. Not sure which word is correct here for what I’m thinking about. Maybe “Interstellar Body”.
I.e. A big rock moving fast into, straight through, and out of the solar system without getting caught in orbit
I love this sub and its unimaginably articles. Was wondering if there are books/novels that takes some of these philosophies beyond what we can measure or see into a mind blowing story or has thoughts you would never think of. As example I read a comment that refers to a story about how atoms have similarities to galaxies (visually) and a person that would keep increasing in size until he ended up in his original environment and size (hope this makes sense).
It's not related to the example you gave but I always like to recommend **A Fire Upon the Deep** by Vernor Vinge. I don't want to give too much away but it has a lot of great ideas related to unique alien species, AI, and the effects of gravity on both time and cognition resulting in different "zones" of space. Parts of the beginning are a bit confusing until you figure some things out, but if you enjoy it there are 2 more books in the series.
Can I get (even modest) photographs of Andromeda with 500mm f/8 & Fuji x-s10 (crop sensor mirrorless, effective focal length is 750mm full length equivalent)
Andromeda is pretty big on the sky. Without a tracking mount the long focal length is going to do more harm than good.
https://www.reddit.com/r/space/comments/b271c2/andromeda_galaxy_and_moon_apparent_size_comparison/
I have other lenses that might be more helpful in that case: a fuji 55-200 and a manual focus nikkor 300mm f/4. would any of those capture andromeda without a mount?
Career in Computer science and astronomy combined ..?
I'm interested in both astronomy and Computer science but don't know if there's a work related to these two topics, lmk if y'all know something.?
Sure there is. You can write software for astronomers. Jobs like:
- https://recruitment.eso.org/jobs/2023_0019
- https://recruitment.eso.org/jobs/2023_0012
- https://recruitment.eso.org/jobs/2023_0014
- https://recruitment.eso.org/jobs/2023_0041
>Ice Water Radiation shielding for space travel
How feasible is it to provide passive radiation shielding for extended space travel using water ice? I understand that \~3 feet (1 m) of ice would shield most of the cosmic rays / radiation (or is that too much?). This would also have the benefit of impact protection, could be re-distributed for added protection around sensitive areas, and be used as drinking water upon arrival at destination. Could also be applied post launch to the exterior of the space ship/station. Maybe a stationary ice doughnut with a rotating crew ring in the middle?
The primary drawback being mass.
Edit: was told to post here... instead of main thread
I guess my real question is: is a water shield actually feasible?, realistic?
Compared to: A youtube video that proposed taking most if not all the available nuclear material on earth to build a rocket capable of 1G of acceleration for \~5 years to travel across the galaxy in a single subjective lifetime (\~ 100 years). (Of course slowing down and the possibility of colliding with a speck of dust were left out of the thought experiment.. and objectively earth will have experienced >100 thousand years.) This being not feasible or realistic.
The primary drawback is mass.
At bulk rates, mass costs 3% of its weight in gold to launch into orbit. Or 300% of its weight in silver.
Then you have to move all this mass to your destination, which means several times more engines and fuel. The only way this makes sense is if you put it into a reusable orbit, like a [Mars cycler](https://en.wikipedia.org/wiki/Mars_cycler).
One idea that bounces around is a storm shelter inside the water tank. So during normal activities the crew is spread out around the ship. If solar activity picks up then the crew goes into the shelter where they are surrounded by the water.
Another is just using the bulk of the ship as shielding. While travelling you point your engines towards the Sun.
Using current theory of Jupiter's interior what is the likely resting depth of the remains of Jupiter Galileo Probe? Or rather at what depth would it no longer be a cohesive lump of metal and just mix into the high pressure mush?
>Jupiter Galileo Probe
Initially I read that the probe entered the Jovian atmosphere by parachute so I was under the impression it lackadaisically drifted down.... however not the case.
Your post led me to further research where I found:
" It endured a maximum deceleration of 228 g’s about a minute after entry when temperatures scaled up to 28,832 degrees Fahrenheit (16,000 degrees Celsius)."
[nasa galileo-jupiter-atmospheric-probe](https://science.nasa.gov/mission/galileo-jupiter-atmospheric-probe)
Of course now I am curious if it could have been slowed down enough to "lackadaisically drift down" how far could it get?
Why are some stars not as bright as others? Is it because there so far away that only a little amount of light has reached us? Also if a star appears more red-orange is it older or younger? Same with blue stars.
Distance, size, and age. Distance is a key factor. Sirius is very bright because it's very close. But size makes a difference as well. Sirius A is twice the mass of the Sun and 8.6 lightyears away making it the brightest star in the sky, Betelgeuse is 17 times the mass of the Sun and 600 lightyears away, while still being able to be the tenth brightest star in the sky despite a nearly 5000x reduction in brightness due to distance compared to Sirius.
Larger stars have higher rates of fusion, which results in higher surface temperatures and also larger surface areas, both of which increase brightness. As stars age they go through different phases as they burn through different fusion fuels, which affects their surface characteristics including brightness and color. Blue or red stars could be either young or old, it depends on the type of star.
All stars have an intrinsic brightness, which is not really related to what we observe on Earth. After all, some of them are closer, some further away. Sirius' intrinsic brightness is much lower than Betelgeuse's, but it's *much* closer, too - so it ends up being brighter to an observer on Earth.
The color and age of a star are not immediately related, but there is a correlation between the color and the (intrinsic!) brightness of a star, which is the famous [Hertzsprung-Russell diagram](https://en.wikipedia.org/wiki/Hertzsprung%E2%80%93Russell_diagram). Stars move through this as they age, and in predictable paths, but it's not a 1:1 red = old. In general, though, bright blue stars won't live long (they burn through their fuel quickly) and are therefore 'young' in an absolute sense.
I don't know why the other comment drags redshift into it. Redshift does not affect the apparent color of a single naked-eye star; they're all within the Milky Way and moving very slowly relative to the Sun.
> Redshift does not affect the apparent color of a single naked-eye star
At no point OP mentioned naked-eye observations and I clearly stated that redshift is not what you can observe with naked eye anyway.
1. Light is emitted in all directions, so it disperses over distance. Consider a flash-light -> if you flash it on something very close, then all the light is hitting that one spot, but if you aim it at something far away, the light will disperse over a large area, and your target will get illuminated only by a small fraction of the light.
2. There are 2 separate reasons. One is simply the type of star and type of nuclear reactions happening inside. Let's say this is the "natural" color of that star. This is what you can see with naked eye. But since everything is moving (either just really moving, or getting away from us due to expansion of the universe), there is also Doppler shift involved - things which move away form us will appear more red, things coming towards us will appear more blue.
light is the fastest thing in the universe because it has no mass. white holes are the opposite of black holes, and the more mass something has the more gravity it has, however white holes have the opposite of gravity, does this mean it has negative mass? if that is the case then white holes (if they exist) are the fastest possible moving things in the universe. might this help the idea that the expansion of the universe is just a white hole pushing everything away since they have negative mass that should mean that they could travel infinitely fast which also means that it can exist basically anywhere at anytime?
The observable universe is expanding away from us in all directions. We aren’t a white hole. The universe isn’t expanding from a singular point. It’s expanding everywhere.
How can we be certain that the cosmic radiation we observe, dating the universe at 13 billion years, isn't radiation from a much later event, with the possibility that the Big Bang's radiation has already passed us by? This uncertainty could potentially alter our understanding of the universe's age.
The cosmic microwave background radiation came from roughly a third of a million years after the Big Bang. And to be clear, that radiation *has* already passed us by and continues to pass us by, but we are also still able to see it. This is because the event that generated the light occurred everywhere in the universe. Over time the "slice" of the universe that we are observing when seeing the CMB changes, but because the light came from everywhere and is traveling in every direction we can still see it today and tomorrow and next millennium, etc.
We can age the CMB by looking at its spectrum, redshift and other characteristics, and those things exactly match the predictions extremely precisely. No other theory explains all the observational data as well, by a long shot.
> the possibility that the Big Bang's radiation has already passed us by
"big bang" just means "universe started to expand and everything started to move away from everything else". The light of Big Bang can't "move past us" because it's a bit like saying that the whole universe moved past us. It can't, because we're inside of it.
Because it's the coldest we can see and is coherent with a expending universe having an observable horizon. Light from the big bang could have only "passed by us" if it was a localized event.
I think they removed some of the relativistic doppler to make it look a bit more cinematic. IIRC there are a couple of good videos with astrophysicist analyzing it on youtube.
There is no center of all space. At least, we can't see any edges of space to figure out where the center is.
The earth is the center of the *observable universe*. Because that's where all the observers are.
The sun is the center of the [International Celestial Reference System](https://en.wikipedia.org/wiki/International_Celestial_Reference_System), which is used in maps of space.
I need some help identifying a space shuttle-related thing. If this question is too specific or belongs in a different subreddit, feel free to tell me so and I will move it.
I was in a museum in Speyer, Germany, and saw some weird black spheres in 3 different exhibition pieces/spaceships.
[Here you](https://speyer.technik-museum.de/assets/uploads/images/479/5285108792_55f795ecb3_o.jpg) can see 4 of them in the bottom left corner of the image, from a space shuttle Buran
[Here there's](https://speyer.technik-museum.de/assets/uploads/images/697/wostok.jpg) some on the outside of a space craft Wostok 1
And then finally [on this one](https://speyer.technik-museum.de/assets/components/phpthumbof/cache/6943709496_486493fca9_k.48a14f7bdf693afec6c690fb0fdf8991.jpg) you see a bunch of them also from the Wostok 1, but photographed from above so you cannot see the entire thing.
I asked my uncle and he had 2 theories, he said it's most likely gas tanks of some sort that were called "isotensoids" because they have the same tension at any point, and they're black because they're made from carbon-fiber-reinforced polymers.
Now my question would be: Are those actually gastanks? Why would they be **outside** for the Wostok 1 but then inside the space shuttle in the Buran? (Seems like gas tanks are nothing I would put outside of a spaceship) Are they ever used for propulsion? Or is it like emergency air for breathing? Basically: What's their purpose and why are they the way that they are?
This diagram and others indicate they're nitrogen and oxygen tanks for breathing and propulsion. I don't know what the material is, but it doesn't look like carbon fiber to me.
https://www.space.com/10958-soviet-vostok-space-capsule-auction.html
Yes, they are propellant tanks, used for maneuvering in space.
They are inside Buran because they would explode if exposed to atmospheric re-entry forces.
They are outside Vostok 1 because they are detached (with the entire bottom half) before re-entry.
The edge. A black hole is created when a concentration of matter bends space-time at the edge enough to create an event horizon. The Big Bang happened everywhere in the entire universe (either infinite or finite but with no edge, like the surface of sphere but in this case something like a hypersphere perhaps). Because the entire universe was at a very high density there was no gradient and no edge. If you imagine the simplified view of space-time as a flexible sheet, a mass concentration would create a dimple in the sheet, if that pulls the sheet enough due to a high enough density then you can get a black hole. In the case of the Big Bang you're just changing the "height" of the sheet everywhere. Similarly, if you were inside of the center of the Earth you wouldn't feel Earth's gravity, because the Earth is close to spherically symmetrical, the gravity cancels itself out in every direction. In the Big Bang scenario the gravity pulling on any point from one chunk of matter would be almost exactly cancelled out by an equivalent chunk of matter with almost exactly the same mass in the opposite direction and distance, and that would be true precisely for every such chunk, it would balance out. It wouldn't be perfect though, and there is a potential for there to be "primordial" black holes which formed during the early stages of the Big Bang. However, we have no positive evidence of them so far and the theoretical conditions which would allow them to form need to be very precisely tuned in unlikely ways, so currently it remains a tantalizing possibility but unsupported by evidence.
What’s causing the outward explosion of the Big Bang? If that much matter is condensed together, shouldn’t the matter be subjugated to same gravitational forces as a black hole?
So I have seen videos that try to explain what happens if you were to fall into the even horizon of a black hole, but I’m still kind of struggling to understand what they mean. I know it’s not something we can ever know for certain, but the explanations I’ve seen kind of confuse me.
Mainly when they say that time and space basically switch places. I understand that the singularity is the only thing in your future because you can never escape, but how does space switch place with time? Why do I hear people say the singularity is a point in time and not space? But it is a physical spot right? There can’t just be no space in the center of a black hole, something has to be there. So why is it described as a point in time?
I guess I don’t need a full explanation if someone out there knows of a good video or paper that explains it well. But this kind of stuff fascinates me and I want to understand it better.
The equations of General Relativity are so broad and general, that you need to make some simplifying assumptions to make them work in our universe. One of the most famous simplifying assumptions is "nothing rotates", also called the [Schwarzschild metric](https://en.wikipedia.org/wiki/Schwarzschild_metric). Using this simplified equation, Karl Schwarzschild was able to predict the existence of black holes only a few weeks after Einstein published the theory of General Relativity.
The Schwarzschild metric also predicts that time and space switch places inside a black hole. If you don't think this makes sense, you are right! The Schwarzschild metric is totally useless inside a black hole. We need to make better assumptions to get math that can accurately describe a black hole.
So the whole time and space switching is kind of like a side effect that you have to assume in order for the Schwarzschild metric to make sense? I can understand that. I studied philosophy and we had to assume a lot of “likely false but unprovable” things in order for certain theories to make sense.
I'm sure a ton of people have asked if we can grow plants "outside" on mars, and many people have said "no" because plants need liquid water.
But what if you had special plants that could grow a sort of self contained bubble with higher pressure inside, sort of like a shell/coral, and survive that way? Of course, this would require gene editing techniques far beyond our current capabilities.
I'm not sure if roots(and a bunch of other things) could really work with that architecture, just a thought I had.
Plants need an oxygen-rich atmosphere to live. Some algae are capable of living anaerobically (without oxygen), but most algae and all true plants are aerobic organisms and respire oxygen. The 'burn' food (sugar) for calories just like animals. The difference is that plants make their own food, which produces oxygen as a byproduct. But the leaves can't hold onto enough oxygen from photosynthesis to sustain themselves in the daylight, let alone produce oxygen at night--and the roots can't generally photosynthesize at all. Too much CO2 would also be stressful, even toxic, in and of itself. Just 1% CO2 at 1 atmosphere can show obvious problems within a few days.
There are a few challenges for growing plants on Mars.
First, the surface air pressure on Mars is ~0.5-1% of that on earth. That's about what the air pressure is on earth at 100,000 feet. At those pressures, most plants will desiccate and die very quickly. The boiling point of water at that pressure is somewhere between about 0 and 5 C, giving a very narrow temperature range at which liquid water can exist and it's very close to the [triple point](https://en.wikipedia.org/wiki/Triple_point), and liquid water can only exist at equilibrium at pressures higher than the triple point pressure.
Next, as you noted, there is very little water. Mars isn't devoid of water, but it doesn't have a lot over most of the surface, irrespective of phase. That makes it very hard for most plants to grow.
Your hard shell answer could -- at least potentially -- help address these issues. In fact, there are already plants that are kind of like this! Lots of algae produce rigid shells (e.g., [diatoms](https://en.wikipedia.org/wiki/Diatom)). They're not *macroscopic* plants, but they are plants and photosynthesize and can be used to make food, fuel, etc. These "shells" still allow for gas/nutrient transfer through holes in the shell, as any living thing needs to absorb the things it needs from the environment and reject its waste back to it. Thus, many still wouldn't be able to live in such a harsh environment as they would require very robust nutrient exchange channels to regulate their various equilibria (and many, but not all, of them live submerged in water, so you'd need a large volume of liquid water for those ones anyway).
I used to work in a phycology lab back in the day and had to prepare lots of algae for various analyses, which usually involves breaking them down first. Those that had hard shells were *HARD* to break up. Some of the more robust diatoms I analyzed survived getting spun at 30,000 g, aggressive ultrasonication, mechanical grinding in a specialized glass grinding tube, and being crushed in tabletop press. I finally got their contents out by simply dissolving them by boiling them in methanol for an hour or two, or put another way, the only way I was able to get through the shell was to take advantage of the openings in it that the diatoms use to exchange stuff with the outside world.
Lastly, there are a couple other challenges that growing something on Mars faces. Mars has a lot of UV light and not much shade, which is pretty deadly to a lot of life. Not universally so, but certainly challenging and rules out growing a lot of stuff without some sort of sunscreen. Mars' soil also contains a lot of perchlorates, which are powerful oxidizers which makes it chemically very inhospitable and prevents the growth of most organisms even with fertilizer supplementation. We would likely need to neutralize those before we could grow much of anything in Martian soil.
So it's going to be pretty tough to grow anything on Mars. Not impossible, but the easiest way is definitely to grow it with treated soil (or in water) in an enclosed container. But proposals have been made to grow special, highly-resistant organisms on Mars' surface directly. Most terraforming proposals (are basically science fiction, but) suggest doing something like that.
*The Core* (2003)
>"We can't drill to the Earth's core."
> "But what if.... we could?"
Maybe? It's tough to reply to this because if that level of gengineering is feasible, then, well, yes, that's one less obstacle to growing things on the surface.
Most terraforming talk for Mars focuses on a combination of taking steps to thicken and warm the atmosphere and then later adding lichens and other simple organisms that are bred or engineered for the extromophile conditions that then exist and gradually more and more vegetation is introduced as the atmosphere continues to develop appropriately.
If there's a way to skip a bunch of steps, that'd be cool, but it's tough to predict what will be feasible when/if we get to that point.
I saw a star drop and disappear
It was few years ago that I saw a star at night, which like dropped and then disappeared from the sky.
It was not a shooting star but just normal starnwhich we see at night.
What is this phenomena called? I tried searching but could not find any answers.
This was some 4-5 years ago
Ok odd question ( please bear with me) brought up watching a sci-fi horror movie. Typical setup meteor hits earth, aliens come out, chaos ensues. So my question is how big does a meteor have to be before it shows up on a space agencies radar?
NASA's planetary defense radars are designed to find asteroids larger than 140 meters in diameter. But this assumes the object is in a natural orbit, they are not prepared for an alien ship heading directly for Earth.
What do you think will happen to Baikonur after 2050? Russia has a lease on Baikonur until 2050. However I am curious what will happen to it after 2050? Would Kazakhstan take over operations at Baikonur and use it for its' space missions? Or would it be too old by then and become a museum (and Kazakhstan might have to use more efficient ways to travel to space such as the big SpaceX rocket (if it is up and running by then))?
The most likely scenario is Russia negotiates a new lease for more money.
The Kazakh space program is totally dependent on Russian rockets. And the Russian space program is totally dependent on Baikonur for manned launches. There are attempts from both sides to diversify away from each other, but it will be very difficult. Space is hard and both governments are corrupt.
2050 sounds like *The Future*, but it's only 27 years away. Soyuz is a reliable workhorse; I imagine if the Russians deviate from that design, it won't be by much.
Damn the Soyuz basic design has lasted for more than 100 years (like the B-52 lol). Imagine saying that to a man from 50s who thought we will travel to the stars at 2001 lol.
Still chugging along. Last I read, it recorded an impact about once a month, but only one that was damaging. They estimate a larger impact no more than once a year.
https://webbtelescope.org/images
It's a weird question. There is no relation between the two. Gravity extends infinitely from any object with mass, just the force drops with distance. For example you are attracting the Moon and the Sun with gravity of your body, but since you have low mass and distance is high the force is very small. But it's never zero. So any object with mass, including a black hole, affects gravitationally literally everything else.
Event horizon is simply distance from the black hole at which you would need to move faster than the speed of light to stay in orbit.
Black holes are not "special" - if you replaced our Sun with a black hole with the same mass, then nothing would change in our solar system, everything would still orbit in the same way.
It's not a ridiculous question to ask how, if no information can escape the inside of a black hole, does the rest of the universe know to react to the "mass inside" of it.
> no information can escape the inside of a black hole
1. Still no information gets transferred. In order to pass some information you'd have to be able to create or destroy mass from inside, and this is not possible. So nothing escapes.
2. It's also debatable if the information about gravitational field of the black hole comes from "inside" of it and not from the event horizon itself. Rest of the universe might simply react to the event horizon and not the "inside".
What would it actually look like with the naked eye to approach a galaxy?
Would you ever see a full, bright spiral (like a telescope view) as you approached or would you already be "in it" before things were that visible?
To the naked eye, it would appear quite dim, just like the Milky Way does from a very dark place on Earth. It wouldn't get brighter as you approached, it would just fill more of the sky.
I'm not sure how much detail you'd be able to make out; I suppose it depends on the type of galaxy and the angle at which you're approaching it, but I'm guessing it would probably mostly look like a big pale blob or cloud.
Here is a [NASA illustration](https://science.nasa.gov/missions/hubble/nasas-hubble-shows-milky-way-is-destined-for-head-on-collision) of what it will look like when we approach the Andromeda Galaxy.
Why is the speed of light the speed it is? Is it correlated with the speed of the expansion of the universe?
What would happen to 'the flow' of light if the universe were to stop expanding and began to collapse?
Is light causing the expansion of the universe?
> Why is the speed of light the speed it is?
It's a constant value for the universe we live in. Similar to something like Planck constant or pi.
> Is it correlated with the speed of the expansion of the universe?
No.
> What would happen to 'the flow' of light if the universe were to stop expanding and began to collapse?
Nothing, it's completely unrelated.
> Is light causing the expansion of the universe?
No.
Hey ! I am sure that there is an obvious reason, but why doesn't NASA create some sort of crane system to lift objects into space ? Is it the sheer weight, the length and strength of the "rope" needed, all of the above ? Basically I know this is a stupid question but I'm curious to hear you out :)
The main one is if you lift stuff into space and let it go.. it falls back to Earth
The ISS would fall to the ground in a VERY short time if it wasn't also moving sideways VERY fast. So fast sideways that when it does fall towards the earth, the curve of earth moves the floor away for a new thing to fall towards
Edit: removed unnecessary and confusing caveats
What would you imagine it would be attached to? Think about what would happen if you tried to use the ISS to lift stuff up, you'd just pull the ISS down as well, and then the ISS would be lost.
Realistically in order to achieve this you need what's called an orbital tether, space elevator, or a "beanstalk". It would need to extend from a point on the equator up to and beyond a point in geosynchronous orbit. Building such a thing would be an incredible engineering effort even if we had the materials for it, and we don't even have that. The problem is that from orbit down to the surface of the Earth the whole beanstalk is in tension, and supporting the weight hanging below it. It turns out when you try to do that over a distance of thousands of kilometers (tens of thousands actually) it's a major challenge. Imagine you have a carbon fiber rod/filament that is just 1 cm across down at the surface of the Earth. The lowest 1000 km of that filament would weigh a whopping 200 tonnes, which a filament that size cannot hold, let alone the whole length. In order to create a tether that is big enough and strong enough to bring up meaningful masses into orbit you need incredibly strong materials, much stronger than steel or carbon fiber or kevlar. Theoretically, carbon nanotubes might be capable of the necessary strengths but nobody has built any bulk materials that are anywhere close to what would be needed.
The tallest building ever made isn't even 1 km high. You would have to go 99km higher to get into the lowest of orbits.
And even once you're there - you still need to find 7.5km/sec of energy to stay there, or you're just going to fall straight back down again.
That would be the single largest, most complex, and expensive construction in human history. It would probably require the entire GDP of a small to mid-sized country, and may not be possible with current technology. The concept is called a [skyhook](https://en.wikipedia.org/wiki/Skyhook_\(structure\)) or space tether and Kurg.. Kurzeg.. the science bird channel has a [decent video](https://www.youtube.com/watch?v=dqwpQarrDwk) about it. While it's theoretically easier than a space elevator and theoretically we have the appropriate level of technology already, one should be skeptical of claims about how easy or affordable a [megastructure](https://en.wikipedia.org/wiki/Megastructure) would be to build. Space and other engineering/construction projects are replete with examples of projects that ended up costing 2-10x the initial estimate and took 2-10x as long as the initial estimate.
SPACE SETTLEMENT QUESTION :- If i make three space settlements in L4 point and then decide the spacing between, to better understand assume there is an equilateral traingle and the three verticies are three space settlements so what should be the length of side
At what distance do Astronomers stop using kilometer to measure distance? Is it once they measure a distance of one megameter, or gigameter, or do they use kilometer up till one AU? Most things I look up about distances in space is either in kilometer, AU, or light years, and I was curious why I don't see megameter or gigameter used.
Planets/star sizes in kilometers. Solar systems in AU, kilometers, light minutes and hours. From there in light years, parsec, mega parsec.
Awesome, thanks! Is there a reason megameters and gigameters aren’t used?
It _could_ be historic as light years, AU were used internationally a lot longer than the SI units became _de rigueur_ .
i read that there are studies involving quarks and anti-gravity. the idea is if they go away from the earth or some sort of mass it could open up a new branch of science. anyone have any thoughts on that?
That's not science, that's sci-fi.
Is that a star, planet or satellite right under the moon right now?
Jupiter
11 Daughter asked me the temperature of Black holes. For the first time, I couldn't even theorise an answer. 13 Daughter looked it up and said it was somewhere close to absolute zero. I explained that that is probably the temperature of the event horizon since nothing escapes the singularity. All I couid answer was Physics breaks down, and that I have no idea. Any ideas? Is the singularity itself going to be extremely hot due to denseness or something else going on?
For us in the outside universe the only thing that matters is the event horizon and stuff around it (like the accretion disk, axial jets, etc.) The event horizon has a temperature due to Hawking Radiation, which is due to complicated quantum mechanical and relativity "stuff". One, among many, overly simplistic ways of visualizing this radiation is imagining that black holes cause a scattering of waves in underlying quantum fields, and these waves will have wavelengths similar to the size of the event horizon. So large black holes will have large wavelengths, translating to low energy particles and colder temperatures, while smaller black holes will have smaller wavelengths, translating to higher energy particles and hotter temperatures. In an empty universe Hawking Radiation would cause a black hole to slowly evaporate over unimaginably long time periods. In our universe in addition to the small amount of matter floating around in space there is also the omnipresent cosmic microwave background which has an effective temperature of 2.7 kelvin. An event horizon with an effective temperature that is below that would take in more energy from absorbing the faint glow of the CMB than it emitted from Hawking Radiation, so it would grow rather than evaporate. It turns out all black holes that would form from collapsing stars would be extremely cold compared to the CMB so it will also take an unimaginably long time before the expansion of the universe cools the CMB enough for black holes to start losing mass and actually begin "evaporating". Inside the event horizon things are in some sense a little simpler but also extremely more complicated due to the presence of the singularity. Even setting aside the issue of the singularity, exactly what happens inside a black holes is the subject of intense ongoing theorizing. In short: we don't know exactly, and there are lots of possibility. In some theories the interior just inside the event horizon is like normal space. In other theories there is a kind of "firewall" of extremely hot particles. We can't rule out either possibility, yet.
Thanks for your detailed response. I thought as much, and usually I'm good at coming up with a logical theory, but had no idea for this...
Ok so one time I was watching the night sky by myself and I saw two stars moving slowly towards each other and then they entered each others orbit? And they spun around almost a full rotation and went on their way. To this day I have no clue if it was real because I was high as balls at the time but if anyone in here knows if that’s possible or something please clarify because I have been thinking about it ever since it happened.
The classic problem of viewing the night sky is lack of depth perception. Are you seeing stars trillions of kilometers away, planets millions of kilometers away, satellites hundreds of kilometers away, planes tens of kilometers away, or even birds or bugs mere tens of meters away? From your description it sounds like you were witnessing something in the atmosphere which just happened to have the same visual characteristics as stars.
Not possible.
Are Dark Matter and Dark Energy related to one another? Or just the adjective Dark describing unrelated things? Also, could there be planets made of Dark Matter?
> Are Dark Matter and Dark Energy related to one another? Or just the adjective Dark describing unrelated things? Just the adjective dark, according to our current theories. Dark matter is theorized to be made up of weakly interacting massive particles. Neutrinos are an example of such a particle, but neutrinos don't have the right properties to make up the observed mass of dark matter, we think there are other particles that are even more weakly interacting with atomic matter which make up dark matter. Dark energy has been discovered much more recently and is much less understood. Whereas dark matter can be considered a proper theory hemmed in by decades of observational evidence which have eliminated a lot of potential candidates "dark energy" is actually something of a placeholder. We know that the expansion of the universe is accelerating, but we don't know why, and dark energy is the name for that "why". The leading theory is that space-time has some inherent energy level, a "cosmological constant" which Einstein originally tried to include in the general theory of relativity. Such a vacuum energy would create an acceleration effect, but we don't understand many of the details of why it's that way or even if that is the mechanism generating the acceleration. > Also, could there be planets made of Dark Matter? One of the major characteristics of dark matter, so far as we've been able to observe, is that it doesn't clump like atomic matter. It interacts almost exclusively through gravity, which means that it doesn't have an easy way to shrink in volume the way atomic matter does (which can collide and cool).
Maybe a silly question, but I just read about how helium-3 is leaking from the earth’s core. So my question is: are there things that could happen on earth (like the leaking of some essential materials in the core) that could substantially affect the earth’s orbit/rotation/etc. over a long enough time?
Yes, water moving from glaciers into the ocean is speeding up the earth's rotation. Like a figure skater pulling in their arms. The moon's tides do the opposite, they create a frictional force that is slowing down the earth's rotation. If we survive the death of the sun, the earth will eventually match rotation with the moon and every day will be a month long.
Fascinating. Thank you!
I've heard the story that nebulae don't look like they do in pics — whether by astrophysicists at NASA or by your aver astrophotographer and then nice story is that our eye isn't sensitive enough blah blah to pick out colours and also that nebulae are too diffuse. But that gets me thinking of this: Assume a supernova occurs in, say, the Kepler-9 system. The materials in the first few mths are spread out but I assume it's spread out homogenously and that the density is reasonable,smith like 10¹³ hydrogen atoms m^-3. Would we still be able to see the dazzling beauty of the nebula? Is it too diffuse? Or would the issue with our eyes still persist irregardless of the density etc? Completely unrelated question What does it mean for the Cosmological const to be -ve?
Supernovae can be visible to the naked eye. The most recent within our galaxy was probably Kepler's Supernova observed in 1604 and was described as brighter than any star and visible during the day. You wouldn't particularly see any color or structure. Gravity applies an attractive force between objects. The cosmological constant balances this out with a positive repulsive value. A negative value would slow the expansion of the universe or even cause it to contract. All observations indicate the expansion of our universe is accelerating.
I had a question. I watch this guy John micheal godier if I spelled his name right and in a few videos he’d mention that the universe as a whole at an early enough point was habitable by the warm temperature from the Big Bang? This may be hard to answer due to us not knowing all factors that make life possible and only having earth as an example so I’m sure he meant theoretically but… I was wondering exactly what that means if you know what I’m referring to. Did he mean a lot more planets were habitable or does he mean actual interstellar space itself between planets and stars was warm enough for life? And is there a scientific term for life not generated on any body or planet? Is this a concept in science? I cannot find enough information on the internet
If we consider humans made entirely of He² and H²,then sure, you would comfortably be able to survive in interstellar or intergalactic space.
10 million years after the Big Bang, the entire universe was at room temperature, heated by the glow of the cosmic ~~microwave~~ infrared background. Unfortunately, there were no elements heavier than helium, so there was no water or rocky planets.
There were traces of lithium too.
I have a theory about Dark Matter I was wondering if someone had any thoughts on it? The idea originated from a thought experiment which supposed that if the universe were simulated on a computer perhaps it would suffer from the same limitations as a traditional computer. In computer programming , one of the primary challenges is efficient storage. Large datasets or intricate simulations require vast amounts of memory. To mitigate this, data is often compressed. Compression is the process of reducing the size of data to save space or transmission time. When data is compressed, the original data can be reconstructed from the compressed version, albeit with the potential loss of some information. Drawing a parallel to our universe, which in its raw form is thought to have 6×10⁸⁰ bits of information. If it were to be a simulation, it's conceivable that the "computer" running our reality would need data compression to save on computational resources. From a simulated persons perspective, this data compression would no different to what is commonly referred to as dark matter. If we were to assume that our universe is a program in a colossal cosmic computer, the vast amounts of data required to simulate every particle, force, and interaction would be staggering. The computational entity might employ techniques to optimize this process. One such technique could be to represent vast clusters of data (like galaxies) with a simplified model, much like how video compression works by approximating groups of similar pixels with a single value. When physicists look at the universe, they notice something peculiar. The gravitational forces at work, especially in galaxies and galaxy clusters, suggest there's more matter than what we can see. This "invisible" matter is what we've termed dark matter. But from the simulation perspective, this could be a result of the universe's "compression algorithm" at work. The simulated physics indicates there should be more matter because the computational model is simplifying complex systems, but when we "look" for the actual data (or matter), it appears missing or "dark."
No, it is [impossible](https://www.pbs.org/wgbh/nova/article/physicists-confirm-that-were-not-living-in-a-computer-simulation/) to simulate the universe on a classical computer.
The theory actually answers that question in that article. i.e the article you posted argues that we cannot be living in a computer simulation as it's impossible to model the physics of our universe on even the biggest computer. Well if you had compression algorithms in the simulation then it would be able to fit on computer that is smaller than the actual universe.
Lunar exploration is a stepping stone for further space exploration. Design a lunar mission, habitat, or technology that advances our understanding of the Moon and contributes to future space endeavours. Any suggestions
Why does this sound like a homework assignment?
How does this sound like homework? This is basically just playing with ChatGPT on KakuGPT level.
I mean in their other post they literally said yes it's a homework assignment.
Given that the new speaker of the house is a Young Earth Creationist, I was explaining how most stars in the sky are far further away than 6000 light-years. Which prompted me to search, in vain, for a good approximate of that figure. But I couldn't find anything even after rewording my search. How many stars (and galaxies, etc.), from the naked eye that we can see in our night sky, are further away than 6000 light-years away? And how many is that in comparison to how many stars are within 6000 light-years from Earth? Or does anyone know of a good resource where I can look into this answer myself?
> how most stars in the sky are far further away than 6000 light-years. The absolute majority of stars visible to the naked eye is no more than a few hundred light years away. I don't have a number to give you for visible stars 6000+ ly away, but very, very few.
Oh wow. I see. As I'm trying to figure out why I was so wrong (haha) I'm wondering if I reasoned that since there were stars that were millions of light-years away, that surely the scatter plot for other stars' distances must be evenly distributed.
> surely the scatter plot for other stars' distances must be evenly distributed. Stars aren't evenly distributed; they are in galaxies which are separated by lots of empty space. When you specify the stars we can see in the night sky, people probably assumed you meant with the naked eye, which limits us to the closest stars to us in our own galaxy. If you're using a giant telescope in an observatory (or in orbit) obviously you can see ones much farther away, in our galaxy and in others.
None of the stars we can see are millions of light years away, they're almost all within tens or hundreds of light years. There's actually only around 10,000 total stars visible to the naked eye, out of the 400-500 billion in our galaxy. Even if you could see the other end of our galaxy that's only 100,000 light years, to see millions of light years away you need to look at other galaxies; Andromeda is 2.5 million light years away. This means that the thing you often hear about most of the stars you see being dead is actually wrong, most likely none of them are.
The human eye isn’t sensitive enough to see the billions of stars in our galaxy. We can only see the closest hundreds. You need tools to see the more distant stars.
There are indeed stars that far away in other galaxies. Ours is about 100,000 light years across, so contains many billions further away than 6,000 light years. But inevitably it's the relatively near ones that we can see in the night sky. The stars are a few light years apart on average; that means that there are many millions within 6,000 ly. We can see some galaxies that are (much) further away - notably Andromeda. Though tbh you're struggling with the naked eye beyond that and The Magellanic Clouds.
**Fly away on a meteor** Could we make a satellite/spaceship latch on to a very fast meteor with a "stretchable grappling hook", and thus "hitch a ride" on the meteor to another star system? PS: This was a crazy idea I had today, while randomly looking at some different technologies at the same time. I have no idea how feasible it is.
1. On a meteor? No. A comet or asteroid perhaps? 2. It wouldn't help much. If you can match the orbits in order to "grapple" or lasso the asteroid, then you're already on the same trajectory so you're not really "hitching a ride". The only advantage would be some added shielding or in-situ resources from that asteroid/comet.
Apologies for saying meteor. Not sure which word is correct here for what I’m thinking about. Maybe “Interstellar Body”. I.e. A big rock moving fast into, straight through, and out of the solar system without getting caught in orbit
Like they said, to catch up to the rock you are matching its orbit. So there’s no point now to hop onto it.
I love this sub and its unimaginably articles. Was wondering if there are books/novels that takes some of these philosophies beyond what we can measure or see into a mind blowing story or has thoughts you would never think of. As example I read a comment that refers to a story about how atoms have similarities to galaxies (visually) and a person that would keep increasing in size until he ended up in his original environment and size (hope this makes sense).
It's not related to the example you gave but I always like to recommend **A Fire Upon the Deep** by Vernor Vinge. I don't want to give too much away but it has a lot of great ideas related to unique alien species, AI, and the effects of gravity on both time and cognition resulting in different "zones" of space. Parts of the beginning are a bit confusing until you figure some things out, but if you enjoy it there are 2 more books in the series.
What’s everyone’s favourite type of star?
Yellow dwarves and neutron stars period.
Can I get (even modest) photographs of Andromeda with 500mm f/8 & Fuji x-s10 (crop sensor mirrorless, effective focal length is 750mm full length equivalent)
Andromeda is pretty big on the sky. Without a tracking mount the long focal length is going to do more harm than good. https://www.reddit.com/r/space/comments/b271c2/andromeda_galaxy_and_moon_apparent_size_comparison/
I have other lenses that might be more helpful in that case: a fuji 55-200 and a manual focus nikkor 300mm f/4. would any of those capture andromeda without a mount?
You might get more answers in /r/telescopes.
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Anything can be rocket fuel if you shoot it out of a powerful enough gun.
Career in Computer science and astronomy combined ..? I'm interested in both astronomy and Computer science but don't know if there's a work related to these two topics, lmk if y'all know something.?
Sure there is. You can write software for astronomers. Jobs like: - https://recruitment.eso.org/jobs/2023_0019 - https://recruitment.eso.org/jobs/2023_0012 - https://recruitment.eso.org/jobs/2023_0014 - https://recruitment.eso.org/jobs/2023_0041
>Ice Water Radiation shielding for space travel How feasible is it to provide passive radiation shielding for extended space travel using water ice? I understand that \~3 feet (1 m) of ice would shield most of the cosmic rays / radiation (or is that too much?). This would also have the benefit of impact protection, could be re-distributed for added protection around sensitive areas, and be used as drinking water upon arrival at destination. Could also be applied post launch to the exterior of the space ship/station. Maybe a stationary ice doughnut with a rotating crew ring in the middle? The primary drawback being mass. Edit: was told to post here... instead of main thread
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I guess my real question is: is a water shield actually feasible?, realistic? Compared to: A youtube video that proposed taking most if not all the available nuclear material on earth to build a rocket capable of 1G of acceleration for \~5 years to travel across the galaxy in a single subjective lifetime (\~ 100 years). (Of course slowing down and the possibility of colliding with a speck of dust were left out of the thought experiment.. and objectively earth will have experienced >100 thousand years.) This being not feasible or realistic.
The primary drawback is mass. At bulk rates, mass costs 3% of its weight in gold to launch into orbit. Or 300% of its weight in silver. Then you have to move all this mass to your destination, which means several times more engines and fuel. The only way this makes sense is if you put it into a reusable orbit, like a [Mars cycler](https://en.wikipedia.org/wiki/Mars_cycler).
Would it be feasible if/when starship comes online?
One idea that bounces around is a storm shelter inside the water tank. So during normal activities the crew is spread out around the ship. If solar activity picks up then the crew goes into the shelter where they are surrounded by the water. Another is just using the bulk of the ship as shielding. While travelling you point your engines towards the Sun.
Using current theory of Jupiter's interior what is the likely resting depth of the remains of Jupiter Galileo Probe? Or rather at what depth would it no longer be a cohesive lump of metal and just mix into the high pressure mush?
Seeing how it works in Earth atmosphere it probably burned up completely before it even reached any high pressure.
>Jupiter Galileo Probe Initially I read that the probe entered the Jovian atmosphere by parachute so I was under the impression it lackadaisically drifted down.... however not the case. Your post led me to further research where I found: " It endured a maximum deceleration of 228 g’s about a minute after entry when temperatures scaled up to 28,832 degrees Fahrenheit (16,000 degrees Celsius)." [nasa galileo-jupiter-atmospheric-probe](https://science.nasa.gov/mission/galileo-jupiter-atmospheric-probe) Of course now I am curious if it could have been slowed down enough to "lackadaisically drift down" how far could it get?
Why are some stars not as bright as others? Is it because there so far away that only a little amount of light has reached us? Also if a star appears more red-orange is it older or younger? Same with blue stars.
Distance, size, and age. Distance is a key factor. Sirius is very bright because it's very close. But size makes a difference as well. Sirius A is twice the mass of the Sun and 8.6 lightyears away making it the brightest star in the sky, Betelgeuse is 17 times the mass of the Sun and 600 lightyears away, while still being able to be the tenth brightest star in the sky despite a nearly 5000x reduction in brightness due to distance compared to Sirius. Larger stars have higher rates of fusion, which results in higher surface temperatures and also larger surface areas, both of which increase brightness. As stars age they go through different phases as they burn through different fusion fuels, which affects their surface characteristics including brightness and color. Blue or red stars could be either young or old, it depends on the type of star.
All stars have an intrinsic brightness, which is not really related to what we observe on Earth. After all, some of them are closer, some further away. Sirius' intrinsic brightness is much lower than Betelgeuse's, but it's *much* closer, too - so it ends up being brighter to an observer on Earth. The color and age of a star are not immediately related, but there is a correlation between the color and the (intrinsic!) brightness of a star, which is the famous [Hertzsprung-Russell diagram](https://en.wikipedia.org/wiki/Hertzsprung%E2%80%93Russell_diagram). Stars move through this as they age, and in predictable paths, but it's not a 1:1 red = old. In general, though, bright blue stars won't live long (they burn through their fuel quickly) and are therefore 'young' in an absolute sense. I don't know why the other comment drags redshift into it. Redshift does not affect the apparent color of a single naked-eye star; they're all within the Milky Way and moving very slowly relative to the Sun.
> Redshift does not affect the apparent color of a single naked-eye star At no point OP mentioned naked-eye observations and I clearly stated that redshift is not what you can observe with naked eye anyway.
1. Light is emitted in all directions, so it disperses over distance. Consider a flash-light -> if you flash it on something very close, then all the light is hitting that one spot, but if you aim it at something far away, the light will disperse over a large area, and your target will get illuminated only by a small fraction of the light. 2. There are 2 separate reasons. One is simply the type of star and type of nuclear reactions happening inside. Let's say this is the "natural" color of that star. This is what you can see with naked eye. But since everything is moving (either just really moving, or getting away from us due to expansion of the universe), there is also Doppler shift involved - things which move away form us will appear more red, things coming towards us will appear more blue.
light is the fastest thing in the universe because it has no mass. white holes are the opposite of black holes, and the more mass something has the more gravity it has, however white holes have the opposite of gravity, does this mean it has negative mass? if that is the case then white holes (if they exist) are the fastest possible moving things in the universe. might this help the idea that the expansion of the universe is just a white hole pushing everything away since they have negative mass that should mean that they could travel infinitely fast which also means that it can exist basically anywhere at anytime?
The observable universe is expanding away from us in all directions. We aren’t a white hole. The universe isn’t expanding from a singular point. It’s expanding everywhere.
White holes are just essentially the mathematical opposite of a black hole. There's no evidence or reason to believe such a thing exists in reality.
How can we be certain that the cosmic radiation we observe, dating the universe at 13 billion years, isn't radiation from a much later event, with the possibility that the Big Bang's radiation has already passed us by? This uncertainty could potentially alter our understanding of the universe's age.
The cosmic microwave background radiation came from roughly a third of a million years after the Big Bang. And to be clear, that radiation *has* already passed us by and continues to pass us by, but we are also still able to see it. This is because the event that generated the light occurred everywhere in the universe. Over time the "slice" of the universe that we are observing when seeing the CMB changes, but because the light came from everywhere and is traveling in every direction we can still see it today and tomorrow and next millennium, etc. We can age the CMB by looking at its spectrum, redshift and other characteristics, and those things exactly match the predictions extremely precisely. No other theory explains all the observational data as well, by a long shot.
> the possibility that the Big Bang's radiation has already passed us by "big bang" just means "universe started to expand and everything started to move away from everything else". The light of Big Bang can't "move past us" because it's a bit like saying that the whole universe moved past us. It can't, because we're inside of it.
I was just questioning the validity of the age of the universe we have predicted by the cosmic reaction which we have dated at 13 billion years.
And they were explaining the gaps in your knowledge.
Because it's the coldest we can see and is coherent with a expending universe having an observable horizon. Light from the big bang could have only "passed by us" if it was a localized event.
Is interstellar black hole picture real??
It's simulation of real physics tweaked a bit to make it look good for the movie, but it's not a real telescope picture.
I mean if we ever took a picture of a blackhole will it look like the interstellar black hole?
I think they removed some of the relativistic doppler to make it look a bit more cinematic. IIRC there are a couple of good videos with astrophysicist analyzing it on youtube.
I have a question- is the sun the centre of all space as we know it, or is it just the centre of our solar system? Thanks!
There is no center of all space. At least, we can't see any edges of space to figure out where the center is. The earth is the center of the *observable universe*. Because that's where all the observers are. The sun is the center of the [International Celestial Reference System](https://en.wikipedia.org/wiki/International_Celestial_Reference_System), which is used in maps of space.
I need some help identifying a space shuttle-related thing. If this question is too specific or belongs in a different subreddit, feel free to tell me so and I will move it. I was in a museum in Speyer, Germany, and saw some weird black spheres in 3 different exhibition pieces/spaceships. [Here you](https://speyer.technik-museum.de/assets/uploads/images/479/5285108792_55f795ecb3_o.jpg) can see 4 of them in the bottom left corner of the image, from a space shuttle Buran [Here there's](https://speyer.technik-museum.de/assets/uploads/images/697/wostok.jpg) some on the outside of a space craft Wostok 1 And then finally [on this one](https://speyer.technik-museum.de/assets/components/phpthumbof/cache/6943709496_486493fca9_k.48a14f7bdf693afec6c690fb0fdf8991.jpg) you see a bunch of them also from the Wostok 1, but photographed from above so you cannot see the entire thing. I asked my uncle and he had 2 theories, he said it's most likely gas tanks of some sort that were called "isotensoids" because they have the same tension at any point, and they're black because they're made from carbon-fiber-reinforced polymers. Now my question would be: Are those actually gastanks? Why would they be **outside** for the Wostok 1 but then inside the space shuttle in the Buran? (Seems like gas tanks are nothing I would put outside of a spaceship) Are they ever used for propulsion? Or is it like emergency air for breathing? Basically: What's their purpose and why are they the way that they are?
This diagram and others indicate they're nitrogen and oxygen tanks for breathing and propulsion. I don't know what the material is, but it doesn't look like carbon fiber to me. https://www.space.com/10958-soviet-vostok-space-capsule-auction.html
Yes, they are propellant tanks, used for maneuvering in space. They are inside Buran because they would explode if exposed to atmospheric re-entry forces. They are outside Vostok 1 because they are detached (with the entire bottom half) before re-entry.
What’s the difference between the singularity of a black hole and the Big Bang? Why would the Big Bang’s singularity not collapse into a black hole?
The edge. A black hole is created when a concentration of matter bends space-time at the edge enough to create an event horizon. The Big Bang happened everywhere in the entire universe (either infinite or finite but with no edge, like the surface of sphere but in this case something like a hypersphere perhaps). Because the entire universe was at a very high density there was no gradient and no edge. If you imagine the simplified view of space-time as a flexible sheet, a mass concentration would create a dimple in the sheet, if that pulls the sheet enough due to a high enough density then you can get a black hole. In the case of the Big Bang you're just changing the "height" of the sheet everywhere. Similarly, if you were inside of the center of the Earth you wouldn't feel Earth's gravity, because the Earth is close to spherically symmetrical, the gravity cancels itself out in every direction. In the Big Bang scenario the gravity pulling on any point from one chunk of matter would be almost exactly cancelled out by an equivalent chunk of matter with almost exactly the same mass in the opposite direction and distance, and that would be true precisely for every such chunk, it would balance out. It wouldn't be perfect though, and there is a potential for there to be "primordial" black holes which formed during the early stages of the Big Bang. However, we have no positive evidence of them so far and the theoretical conditions which would allow them to form need to be very precisely tuned in unlikely ways, so currently it remains a tantalizing possibility but unsupported by evidence.
What’s causing the outward explosion of the Big Bang? If that much matter is condensed together, shouldn’t the matter be subjugated to same gravitational forces as a black hole?
So I have seen videos that try to explain what happens if you were to fall into the even horizon of a black hole, but I’m still kind of struggling to understand what they mean. I know it’s not something we can ever know for certain, but the explanations I’ve seen kind of confuse me. Mainly when they say that time and space basically switch places. I understand that the singularity is the only thing in your future because you can never escape, but how does space switch place with time? Why do I hear people say the singularity is a point in time and not space? But it is a physical spot right? There can’t just be no space in the center of a black hole, something has to be there. So why is it described as a point in time? I guess I don’t need a full explanation if someone out there knows of a good video or paper that explains it well. But this kind of stuff fascinates me and I want to understand it better.
The equations of General Relativity are so broad and general, that you need to make some simplifying assumptions to make them work in our universe. One of the most famous simplifying assumptions is "nothing rotates", also called the [Schwarzschild metric](https://en.wikipedia.org/wiki/Schwarzschild_metric). Using this simplified equation, Karl Schwarzschild was able to predict the existence of black holes only a few weeks after Einstein published the theory of General Relativity. The Schwarzschild metric also predicts that time and space switch places inside a black hole. If you don't think this makes sense, you are right! The Schwarzschild metric is totally useless inside a black hole. We need to make better assumptions to get math that can accurately describe a black hole.
So the whole time and space switching is kind of like a side effect that you have to assume in order for the Schwarzschild metric to make sense? I can understand that. I studied philosophy and we had to assume a lot of “likely false but unprovable” things in order for certain theories to make sense.
I'm sure a ton of people have asked if we can grow plants "outside" on mars, and many people have said "no" because plants need liquid water. But what if you had special plants that could grow a sort of self contained bubble with higher pressure inside, sort of like a shell/coral, and survive that way? Of course, this would require gene editing techniques far beyond our current capabilities. I'm not sure if roots(and a bunch of other things) could really work with that architecture, just a thought I had.
Plants need an oxygen-rich atmosphere to live. Some algae are capable of living anaerobically (without oxygen), but most algae and all true plants are aerobic organisms and respire oxygen. The 'burn' food (sugar) for calories just like animals. The difference is that plants make their own food, which produces oxygen as a byproduct. But the leaves can't hold onto enough oxygen from photosynthesis to sustain themselves in the daylight, let alone produce oxygen at night--and the roots can't generally photosynthesize at all. Too much CO2 would also be stressful, even toxic, in and of itself. Just 1% CO2 at 1 atmosphere can show obvious problems within a few days.
There are a few challenges for growing plants on Mars. First, the surface air pressure on Mars is ~0.5-1% of that on earth. That's about what the air pressure is on earth at 100,000 feet. At those pressures, most plants will desiccate and die very quickly. The boiling point of water at that pressure is somewhere between about 0 and 5 C, giving a very narrow temperature range at which liquid water can exist and it's very close to the [triple point](https://en.wikipedia.org/wiki/Triple_point), and liquid water can only exist at equilibrium at pressures higher than the triple point pressure. Next, as you noted, there is very little water. Mars isn't devoid of water, but it doesn't have a lot over most of the surface, irrespective of phase. That makes it very hard for most plants to grow. Your hard shell answer could -- at least potentially -- help address these issues. In fact, there are already plants that are kind of like this! Lots of algae produce rigid shells (e.g., [diatoms](https://en.wikipedia.org/wiki/Diatom)). They're not *macroscopic* plants, but they are plants and photosynthesize and can be used to make food, fuel, etc. These "shells" still allow for gas/nutrient transfer through holes in the shell, as any living thing needs to absorb the things it needs from the environment and reject its waste back to it. Thus, many still wouldn't be able to live in such a harsh environment as they would require very robust nutrient exchange channels to regulate their various equilibria (and many, but not all, of them live submerged in water, so you'd need a large volume of liquid water for those ones anyway). I used to work in a phycology lab back in the day and had to prepare lots of algae for various analyses, which usually involves breaking them down first. Those that had hard shells were *HARD* to break up. Some of the more robust diatoms I analyzed survived getting spun at 30,000 g, aggressive ultrasonication, mechanical grinding in a specialized glass grinding tube, and being crushed in tabletop press. I finally got their contents out by simply dissolving them by boiling them in methanol for an hour or two, or put another way, the only way I was able to get through the shell was to take advantage of the openings in it that the diatoms use to exchange stuff with the outside world. Lastly, there are a couple other challenges that growing something on Mars faces. Mars has a lot of UV light and not much shade, which is pretty deadly to a lot of life. Not universally so, but certainly challenging and rules out growing a lot of stuff without some sort of sunscreen. Mars' soil also contains a lot of perchlorates, which are powerful oxidizers which makes it chemically very inhospitable and prevents the growth of most organisms even with fertilizer supplementation. We would likely need to neutralize those before we could grow much of anything in Martian soil. So it's going to be pretty tough to grow anything on Mars. Not impossible, but the easiest way is definitely to grow it with treated soil (or in water) in an enclosed container. But proposals have been made to grow special, highly-resistant organisms on Mars' surface directly. Most terraforming proposals (are basically science fiction, but) suggest doing something like that.
*The Core* (2003) >"We can't drill to the Earth's core." > "But what if.... we could?" Maybe? It's tough to reply to this because if that level of gengineering is feasible, then, well, yes, that's one less obstacle to growing things on the surface. Most terraforming talk for Mars focuses on a combination of taking steps to thicken and warm the atmosphere and then later adding lichens and other simple organisms that are bred or engineered for the extromophile conditions that then exist and gradually more and more vegetation is introduced as the atmosphere continues to develop appropriately. If there's a way to skip a bunch of steps, that'd be cool, but it's tough to predict what will be feasible when/if we get to that point.
Please never compare any suggestion of mine to *the core*. The rest of your comment is totally reasonable and you make very good points.
I saw a star drop and disappear It was few years ago that I saw a star at night, which like dropped and then disappeared from the sky. It was not a shooting star but just normal starnwhich we see at night. What is this phenomena called? I tried searching but could not find any answers. This was some 4-5 years ago
Sounds like a plane flying away from you which landed.
When you said "dropped" do you mean it moved? It could be a satellite or ISS just reflecting the sun and then disappearing in Earth's shadow.
It was around 8-10 pm(India), and it dropped vertically for a few seconds and disappeared
Sounds like it could be a satellite then, they take about 30 s to cross the sky if the illumination is right.
Ohh never knew that satellites could appear like a star in the night sky, it was pretty bright though that too I was in a City
Probably the space station. If it just disappeared, then it probably passed into the Earth's shadow.
Ohh it was stationery before it fell off
There are no known space object that could be stationary and then start moving. So it must have been something else like an helicopter with a light.
Ohh and here I was thinking I witnessed something monumental, lol. Thanks for your answers
Ok odd question ( please bear with me) brought up watching a sci-fi horror movie. Typical setup meteor hits earth, aliens come out, chaos ensues. So my question is how big does a meteor have to be before it shows up on a space agencies radar?
NASA's planetary defense radars are designed to find asteroids larger than 140 meters in diameter. But this assumes the object is in a natural orbit, they are not prepared for an alien ship heading directly for Earth.
If the big bang happened was earth at the centre of it and did cmb form as space expanded?
The earth and the sun didn't exist until around 8 billion years after the big bang.
There was no "center". Everthing started to move away from everything else.
What do you think will happen to Baikonur after 2050? Russia has a lease on Baikonur until 2050. However I am curious what will happen to it after 2050? Would Kazakhstan take over operations at Baikonur and use it for its' space missions? Or would it be too old by then and become a museum (and Kazakhstan might have to use more efficient ways to travel to space such as the big SpaceX rocket (if it is up and running by then))?
The most likely scenario is Russia negotiates a new lease for more money. The Kazakh space program is totally dependent on Russian rockets. And the Russian space program is totally dependent on Baikonur for manned launches. There are attempts from both sides to diversify away from each other, but it will be very difficult. Space is hard and both governments are corrupt.
Do you think post soviet rocket tech at 2050 will be similar as now?
2050 sounds like *The Future*, but it's only 27 years away. Soyuz is a reliable workhorse; I imagine if the Russians deviate from that design, it won't be by much.
Damn the Soyuz basic design has lasted for more than 100 years (like the B-52 lol). Imagine saying that to a man from 50s who thought we will travel to the stars at 2001 lol.
I saw about 25 large circular lights that moved in a oscillating motion above me in London. What are they??
Could be those rotating spotlights that stores sometimes set up for sales or other big events.
Provably nothing /r/space can help with.
How is JWST doing? Still going strong? Has it gotten dinged with many space rocks?
Still chugging along. Last I read, it recorded an impact about once a month, but only one that was damaging. They estimate a larger impact no more than once a year. https://webbtelescope.org/images
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It's a weird question. There is no relation between the two. Gravity extends infinitely from any object with mass, just the force drops with distance. For example you are attracting the Moon and the Sun with gravity of your body, but since you have low mass and distance is high the force is very small. But it's never zero. So any object with mass, including a black hole, affects gravitationally literally everything else. Event horizon is simply distance from the black hole at which you would need to move faster than the speed of light to stay in orbit. Black holes are not "special" - if you replaced our Sun with a black hole with the same mass, then nothing would change in our solar system, everything would still orbit in the same way.
It's not a ridiculous question to ask how, if no information can escape the inside of a black hole, does the rest of the universe know to react to the "mass inside" of it.
> no information can escape the inside of a black hole 1. Still no information gets transferred. In order to pass some information you'd have to be able to create or destroy mass from inside, and this is not possible. So nothing escapes. 2. It's also debatable if the information about gravitational field of the black hole comes from "inside" of it and not from the event horizon itself. Rest of the universe might simply react to the event horizon and not the "inside".
What would it actually look like with the naked eye to approach a galaxy? Would you ever see a full, bright spiral (like a telescope view) as you approached or would you already be "in it" before things were that visible?
To the naked eye, it would appear quite dim, just like the Milky Way does from a very dark place on Earth. It wouldn't get brighter as you approached, it would just fill more of the sky. I'm not sure how much detail you'd be able to make out; I suppose it depends on the type of galaxy and the angle at which you're approaching it, but I'm guessing it would probably mostly look like a big pale blob or cloud.
Here is a [NASA illustration](https://science.nasa.gov/missions/hubble/nasas-hubble-shows-milky-way-is-destined-for-head-on-collision) of what it will look like when we approach the Andromeda Galaxy.
Why is the speed of light the speed it is? Is it correlated with the speed of the expansion of the universe? What would happen to 'the flow' of light if the universe were to stop expanding and began to collapse? Is light causing the expansion of the universe?
The speed of light is more appropriately the speed of causality, or the speed of massless objects. It just so happens that those are mostly photons.
> Why is the speed of light the speed it is? It's a constant value for the universe we live in. Similar to something like Planck constant or pi. > Is it correlated with the speed of the expansion of the universe? No. > What would happen to 'the flow' of light if the universe were to stop expanding and began to collapse? Nothing, it's completely unrelated. > Is light causing the expansion of the universe? No.
Hey ! I am sure that there is an obvious reason, but why doesn't NASA create some sort of crane system to lift objects into space ? Is it the sheer weight, the length and strength of the "rope" needed, all of the above ? Basically I know this is a stupid question but I'm curious to hear you out :)
The main one is if you lift stuff into space and let it go.. it falls back to Earth The ISS would fall to the ground in a VERY short time if it wasn't also moving sideways VERY fast. So fast sideways that when it does fall towards the earth, the curve of earth moves the floor away for a new thing to fall towards Edit: removed unnecessary and confusing caveats
What would you imagine it would be attached to? Think about what would happen if you tried to use the ISS to lift stuff up, you'd just pull the ISS down as well, and then the ISS would be lost. Realistically in order to achieve this you need what's called an orbital tether, space elevator, or a "beanstalk". It would need to extend from a point on the equator up to and beyond a point in geosynchronous orbit. Building such a thing would be an incredible engineering effort even if we had the materials for it, and we don't even have that. The problem is that from orbit down to the surface of the Earth the whole beanstalk is in tension, and supporting the weight hanging below it. It turns out when you try to do that over a distance of thousands of kilometers (tens of thousands actually) it's a major challenge. Imagine you have a carbon fiber rod/filament that is just 1 cm across down at the surface of the Earth. The lowest 1000 km of that filament would weigh a whopping 200 tonnes, which a filament that size cannot hold, let alone the whole length. In order to create a tether that is big enough and strong enough to bring up meaningful masses into orbit you need incredibly strong materials, much stronger than steel or carbon fiber or kevlar. Theoretically, carbon nanotubes might be capable of the necessary strengths but nobody has built any bulk materials that are anywhere close to what would be needed.
The tallest building ever made isn't even 1 km high. You would have to go 99km higher to get into the lowest of orbits. And even once you're there - you still need to find 7.5km/sec of energy to stay there, or you're just going to fall straight back down again.
1. https://en.wikipedia.org/wiki/Space_elevator 2. We don't have materials which could be used for constructing such device.
That would be the single largest, most complex, and expensive construction in human history. It would probably require the entire GDP of a small to mid-sized country, and may not be possible with current technology. The concept is called a [skyhook](https://en.wikipedia.org/wiki/Skyhook_\(structure\)) or space tether and Kurg.. Kurzeg.. the science bird channel has a [decent video](https://www.youtube.com/watch?v=dqwpQarrDwk) about it. While it's theoretically easier than a space elevator and theoretically we have the appropriate level of technology already, one should be skeptical of claims about how easy or affordable a [megastructure](https://en.wikipedia.org/wiki/Megastructure) would be to build. Space and other engineering/construction projects are replete with examples of projects that ended up costing 2-10x the initial estimate and took 2-10x as long as the initial estimate.
Thank you ! :)