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Although the Moon is much closer and "right there" for us, it's subject to numerous meteoric incidents, some of which are disastrous enough to wipe out any sett

Although the Moon is much closer and "right there" for us, it's subject to numerous meteoric incidents, some of which are disastrous enough to wipe out any settlement we set up there. Moreover, only half of the Moon sees the light of the Sun. This fact alone reduces available surface for settlements to only half of the Moon. While the Moon could be a temporary backup plan, in the long-term, you're going to need to terraform a planet and make a suitable atmosphere, both of which are not possible to do to the Moon. Edit: Thanks to the commentators below who mentioned that while the Moon is tidally locked to the Earth, most of its surface does indeed receive light from the Sun. Only one question though: If that is true, then why do they call it "the dark side of the Moon"? (Honest question)

omellet 9y ago
It's tidally locked, so you couldn't you put the settlement on the Earth-facing side and not have to worry as much about meteors?
- antaviana 9y ago
  Well, it's like holding a shield of a radius of only 6,371 km with an arm of 384,400 km long. Or to put it in human terms, like holding a shield of 1.25 cm of radius with your arm of 75 cm. It will not protect you really very much.
- holtalanm 9y ago
  I was thinking the same thing. Earth will shield the moon on the Earth-side, mostly.
- christophilus 9y ago
  That seems to make sense, but if you look at the moon from Earth, you see an awful lot of craters...
jgh 9y ago
> Moreover, only half of the Moon sees the light of the Sun. I'm no astronomer but the moon is tidally locked to the earth and not the sun, which means that the moon should have sunrises/sunsets...
- drostie 9y ago
  Yeah, it does. The real concern is that the moon-day is a full month long and there is no atmosphere transferring heat; any permanent structures on the surface will get very very cold during those two weeks in the dark. If we don't solve this with suitable solar-charged batteries we would need multiple outposts -- say 4 of them dotted around the Moon -- with colonists rotating through the cities to stay in the Sun. But that's also kind of a non-starter because the distance between those cities is something akin to the distance between Denver and New York City -- it's not impossible but it's also a nontrivial drive to be doing every week just to remain in the sunshine.
  - WalterBright 9y ago
    Put a couple large mirrors in orbit around the moon.
    - WalterBright 9y ago
      So, why wouldn't a parabolic mirror in orbit that bounces the light down to solar arrays on the moonbase work?
  - aaronblohowiak 9y ago
    Why not poles?
    - drostie 9y ago
      I'm glad you asked! So there's an important physics reason why the equator is warm and the North and South poles are cold on this planet, and it has to do with how you point a surface. If you ever find yourself in a dark office with a bright desk lamp (or maybe your home office or kid's bedroom might be suitable) you might even try this experiment: take a flat surface, a notepad or steno pad, and hold it up facing the light source, then slowly tilt it away and look at the color of the surface; you'll notice that it doesn't sharply transition from illuminated at 0 degrees to dark at 90 degrees -- instead it smoothly varies like the cosine of that angle. This mathematical effect is incredibly important, it means that sunlight, during the day, averages out to being half as strong as its maximum over the whole of the Earth's surface. The calculation isn't even particularly difficult: the surface area of a sphere is well-known to be 4πr², half of that or 2πr² is illuminated at any one time, but the actual irradiation that we receive is proportional to the cross-section area, which is just the area of the circle: πr². So if the Sun-directly-overhead light were to be illuminating that entire half of the world, we would get k·2πr² light for some k, but instead we only get k·πr² light for that same k, so it works out to be 1/2 when averaged over the whole surface of the Earth. While I was at university a fellow student asked me to guess the coldest place in the Solar System. I guessed "the middle of the dark side of Mercury." I guessed this for a couple reasons: (1) I knew I needed a rock without an atmosphere since atmospheres sustain convection currents that transmit energy, and (2) I figured since Mercury is so close to the Sun it's probably tidally locked to the Sun and therefore this part probably has not seen a speck of sunlight in millions of years. It turns out that general relativity makes point #2 wrong and my friend gleefully informed me that he was looking at an article (there were many, so let's take [1] as representative) suggesting that it might be in a crater on the South pole of the Moon. This has basically the same reasoning of (1) and (2) above, except substituting the shadow of a crater for the shadow of tidal locking. But Mercury is still in the running -- the only issue is that we might not be looking at the dark side of it, but rather, again, at its poles. [1] https://www.space.com/7311-moon-craters-coldest-place-solar-system.html https://www.space.com/7311-moon-craters-coldest-place-solar-...
Zancarius 9y ago
> Moreover, only half of the Moon sees the light of the Sun. What do you mean by this? The moon is tidally locked to the Earth, but the entire surface sees sunlight over the course of ~a month with the exception of a handful of polar craters where small portions are perpetually in shadow.
- vl 9y ago
  Factually this is correct: only half of any planet in the solar system sees light of the Sun at any given moment. :)
  - Zancarius 9y ago
    Only with a literalist interpretation of said fact. :)
michaelwu 9y ago
> Moreover, only half of the Moon sees the light of the Sun That's not true. There is a side of the Moon that's always facing away from us on Earth but each side of the Moon actually gets about 2 weeks of sunlight followed by 2 weeks of darkness.
Arnavion 9y ago
>If that is true, then why do they call it "the dark side of the Moon"? It's the side we can't see from Earth. It's dark as in unreachable by line of sight or light, eg radio communication, from Earth. "Far side of the moon" is the preferred term but "dark side" is popular and persists.
sqeaky 9y ago
> Only one question though: If that is true, then why do they call it "the dark side of the Moon"? This doesn't refer to sunlight, it refers to radio communications. The back of the Moon, relative to Earth cannot receive any kind of signal we can send without some kind of artificial relay. Because the moon it tidally locked with the Earth the same side always faces us. So the back side is always dark to our radio even though it has about a 28 earth long "day". Any (non-polar) spot on the Moon gets about 14 Earth days of light and then another 14 of darkness, corresponding with the phases of the moon we see here.
tambourine_man 9y ago
As others have said, a Moon's day lasts about an Earth's month. There's hope for light most of the year at the poles: https://en.wikipedia.org/wiki/Peak_of_eternal_light https://en.wikipedia.org/wiki/Peak_of_eternal_light I used to fantasize about exploiting the temperature gradient between hemispheres for generating electricity on worlds with long days like Mercury and the Moon when I was a kid.
valuearb 9y ago
Mars is immune to large meteors (actually asteroids)? When did this happen?
HateInAPuddle 9y ago
> then why do they call it "the dark side of the Moon"? Because four billion wordwide population - all living - have a Computer God Containment Policy Brain Bank Brain, a real brain, in the Brain Bank Cities on the far side of the moon we never see.

omellet 9y ago

It's tidally locked, so you couldn't you put the settlement on the Earth-facing side and not have to worry as much about meteors?

antaviana 9y ago
Well, it's like holding a shield of a radius of only 6,371 km with an arm of 384,400 km long. Or to put it in human terms, like holding a shield of 1.25 cm of radius with your arm of 75 cm. It will not protect you really very much.
holtalanm 9y ago
I was thinking the same thing. Earth will shield the moon on the Earth-side, mostly.
christophilus 9y ago
That seems to make sense, but if you look at the moon from Earth, you see an awful lot of craters...

jgh 9y ago

> Moreover, only half of the Moon sees the light of the Sun. I'm no astronomer but the moon is tidally locked to the earth and not the sun, which means that the moon should have sunrises/sunsets...

drostie 9y ago
Yeah, it does. The real concern is that the moon-day is a full month long and there is no atmosphere transferring heat; any permanent structures on the surface will get very very cold during those two weeks in the dark. If we don't solve this with suitable solar-charged batteries we would need multiple outposts -- say 4 of them dotted around the Moon -- with colonists rotating through the cities to stay in the Sun. But that's also kind of a non-starter because the distance between those cities is something akin to the distance between Denver and New York City -- it's not impossible but it's also a nontrivial drive to be doing every week just to remain in the sunshine.
- WalterBright 9y ago
  Put a couple large mirrors in orbit around the moon.
  - WalterBright 9y ago
    So, why wouldn't a parabolic mirror in orbit that bounces the light down to solar arrays on the moonbase work?
- aaronblohowiak 9y ago
  Why not poles?
  - drostie 9y ago
    I'm glad you asked! So there's an important physics reason why the equator is warm and the North and South poles are cold on this planet, and it has to do with how you point a surface. If you ever find yourself in a dark office with a bright desk lamp (or maybe your home office or kid's bedroom might be suitable) you might even try this experiment: take a flat surface, a notepad or steno pad, and hold it up facing the light source, then slowly tilt it away and look at the color of the surface; you'll notice that it doesn't sharply transition from illuminated at 0 degrees to dark at 90 degrees -- instead it smoothly varies like the cosine of that angle. This mathematical effect is incredibly important, it means that sunlight, during the day, averages out to being half as strong as its maximum over the whole of the Earth's surface. The calculation isn't even particularly difficult: the surface area of a sphere is well-known to be 4πr², half of that or 2πr² is illuminated at any one time, but the actual irradiation that we receive is proportional to the cross-section area, which is just the area of the circle: πr². So if the Sun-directly-overhead light were to be illuminating that entire half of the world, we would get k·2πr² light for some k, but instead we only get k·πr² light for that same k, so it works out to be 1/2 when averaged over the whole surface of the Earth. While I was at university a fellow student asked me to guess the coldest place in the Solar System. I guessed "the middle of the dark side of Mercury." I guessed this for a couple reasons: (1) I knew I needed a rock without an atmosphere since atmospheres sustain convection currents that transmit energy, and (2) I figured since Mercury is so close to the Sun it's probably tidally locked to the Sun and therefore this part probably has not seen a speck of sunlight in millions of years. It turns out that general relativity makes point #2 wrong and my friend gleefully informed me that he was looking at an article (there were many, so let's take [1] as representative) suggesting that it might be in a crater on the South pole of the Moon. This has basically the same reasoning of (1) and (2) above, except substituting the shadow of a crater for the shadow of tidal locking. But Mercury is still in the running -- the only issue is that we might not be looking at the dark side of it, but rather, again, at its poles. [1] https://www.space.com/7311-moon-craters-coldest-place-solar-system.html https://www.space.com/7311-moon-craters-coldest-place-solar-...

Zancarius 9y ago

> Moreover, only half of the Moon sees the light of the Sun. What do you mean by this? The moon is tidally locked to the Earth, but the entire surface sees sunlight over the course of ~a month with the exception of a handful of polar craters where small portions are perpetually in shadow.

vl 9y ago
Factually this is correct: only half of any planet in the solar system sees light of the Sun at any given moment. :)
- Zancarius 9y ago
  Only with a literalist interpretation of said fact. :)

michaelwu 9y ago

> Moreover, only half of the Moon sees the light of the Sun That's not true. There is a side of the Moon that's always facing away from us on Earth but each side of the Moon actually gets about 2 weeks of sunlight followed by 2 weeks of darkness.

Arnavion 9y ago

>If that is true, then why do they call it "the dark side of the Moon"? It's the side we can't see from Earth. It's dark as in unreachable by line of sight or light, eg radio communication, from Earth. "Far side of the moon" is the preferred term but "dark side" is popular and persists.

sqeaky 9y ago

> Only one question though: If that is true, then why do they call it "the dark side of the Moon"? This doesn't refer to sunlight, it refers to radio communications. The back of the Moon, relative to Earth cannot receive any kind of signal we can send without some kind of artificial relay. Because the moon it tidally locked with the Earth the same side always faces us. So the back side is always dark to our radio even though it has about a 28 earth long "day". Any (non-polar) spot on the Moon gets about 14 Earth days of light and then another 14 of darkness, corresponding with the phases of the moon we see here.

tambourine_man 9y ago

As others have said, a Moon's day lasts about an Earth's month. There's hope for light most of the year at the poles: https://en.wikipedia.org/wiki/Peak_of_eternal_light https://en.wikipedia.org/wiki/Peak_of_eternal_light I used to fantasize about exploiting the temperature gradient between hemispheres for generating electricity on worlds with long days like Mercury and the Moon when I was a kid.

valuearb 9y ago

Mars is immune to large meteors (actually asteroids)? When did this happen?

HateInAPuddle 9y ago

> then why do they call it "the dark side of the Moon"? Because four billion wordwide population - all living - have a Computer God Containment Policy Brain Bank Brain, a real brain, in the Brain Bank Cities on the far side of the moon we never see.