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Apparent brightness follows an inverse square law. This means an object 130,000 times farther away is only 1/130000² = 0.000000000059 times as bright.

There are other issues caused by the expansion of the universe. You can't see galaxies from 13 billion years ago with a telescope like Hubble, because the galaxies are moving so fast that they are redshifted out of the visible light range. JWST is special because it can see these galaxies in infrared.

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It should be pretty obvious. You are able to look in real time at Jupiter and it’s moons. Webb looked at a single point for 12h to capture those galaxies. Hubble had to look for over 100h to take the deep field image. The human eye can’t collect light for 12h to create an image. The eye also only sees visible light so everything Webb sees is invisible to us.

Brightness falls off exponentially with distance.

Basically not at all. The brightest things in the universe easily outshine whole galaxies despite being star size or a bit larger. Andromeda is only 4 million light years away but it’s too dim to see without a telescope. Can’t get past the inverse square law.

Your main point is correct, but you can see Andromeda with the naked eye on a clear and dark night. It is 2.5 million light years away and It is the only spiral galaxy (other than our own) visible to the naked eye.

So some of my relatives have started asking for my christmas list and as space is my main interest, what sort of space related presents are there around £25

There's a lot of great books out there depending on what you like.

There's also clothing or other small things like mission patches or pins released for specific missions.

Another cool thing might be rocket/spacecraft model kits.

If you're into gaming and haven't played it yet, maybe Kerbal Space Program. Back in undergrad, I had a professor in orbital mechanics highly recommend the game to us to build an intuition before we dived into the math of everything. It's honestly a fantastic way to learn about how space travel works, and it's a lot of fun!

Hello I would love to start my journey with astronomy. I would love to buy a telescope to observe stars such as our Sun or other starts in Milky way. My budget is 2000zł (400$). Thanks in advance for all answers.

I was wondering how pervasive radiation, at levels dangerous to humans, is throughout the galaxy and what discussion there has been about the implications for space travel in the future.

Thanks for the response. I do already have KSP, amazing game although I probably should focus more on the space aspect rather than missiles to blow up the space centre. What specific books would you recommend?

Can depend on what you're interested in. There's lots of books on various celestial bodies or overviews of cosmology/astrophysics. A common goto is "a brief history of time" by Stephen hawking. I havent read that in a long time, but in middle/high school I really liked it.

There's also mission/program specific books like "Chasing New Horizons" (about the New Horizons mission to Pluto), or "Failure is not an Option" by Gene Kranz. Plus tons of biographies in various figures in space.

The most dangerous radiation comes from outside the solar system and is called "galactic cosmic radiation". GCR is ionized hydrogen and helium atoms that are traveling very fast. It will destroy any DNA it hits, which is bad for humans.

There are four levels of GCR:

• On the ground. 100km of air gives very good protection. GCR is not a significant health threat.
• In low earth orbit. The earth's magnetic field gives some protection. We have measured increased cancer risk and cell damage from GCR in astronauts on the International Space Station.
• In the solar system. GCR is a significant threat to people traveling to other planets. Our current calculations are that most people will survive the trip, but some will get cancer and die.
• Outside the solar system. GCR is 10x higher outside the solar system. When you combine this with long travel times, an unshielded spaceship is a death trap. An interstellar spaceship would need a lot of radiation shielding.

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Thank you so much for your comprehensive answer. Do you think this issue would make interstellar travel all but impossible? Is shielding from radiation typically lead in composition (like the lead aprons they give you for medical X-rays), or are there other kinds or technologies? I would imagine that lifting lead into space for this purpose would be prohibitively expensive.

> Do you think this issue would make interstellar travel all but impossible?

No, I don't believe so. The major hurdle to be solved is developing much, much more efficient engines. Radiation shielding has pretty good solutions already.

> Is shielding from radiation typically lead in composition (like the lead aprons they give you for medical X-rays), or are there other kinds or technologies?

The best material depends on the kind of radiation. For X-rays and the like (relatively low energy), lead works great. For galactic cosmic rays containing lots of proton and neutrons, things with a high hydrogen content (like polyethylene plastic) can work better and weigh less.

Water is also an excellent choice: It's decent at radiation protection and the ship will need a lot of it anyway (for drinking, cooling, growing food, possibly for the engines). Lining the outer hull with a layer of water could work. Or the ship could have a radiation vault encased in a thicker layer of water for the crew to take shelter in.

> I would imagine that lifting lead into space for this purpose would be prohibitively expensive.

The whole ship would be much, much heavier than the lining alone. If it is too expensive to launch the ship, dropping a bit of shielding mass won't make much of a difference. Without a breakthrough in the launch cost to Earth orbit, even regular interplanetary travel remains a pipe dream. SpaceX's Starship program aims to change that in the near future.

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Could your question be interpreted as "even though it specifically says 5.01 years, what if maybe it's actually 5.00 years and the 1 was added for funsies"?

No, a period of 5 years means it also gets close to Jupiter. This will destabilize any resonance it creates with Earth.

There may be a more complicated resonance with Earth, Mars, and Jupiter. But there is no reason to believe this would have a period of exactly 5 years.

>>Radiation shielding has pretty good solutions already.

How much time could someone spend unshielded without significant effects? Like time spent space walking to fix something .

Do you think we would see a negative effect on earth if we brought back too many resources from space and in turn added more mass to the planet?