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Comment by whitehexagon | Hacker News Reader

I wonder if there are locations along the dark side / light side border, where some of this water boils off during the 'daytime' heat, and then freezes again during darkness, and is just sitting on the surface as a fine layer of frozen crystals? I know there in very little atmosphere, but maybe just enough to hold a little water vapor? Maybe over time this would allow more accumulation in permanently shaded parts of the lunar landscape, including of course the dark side.

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Reminder that the moon does not have a "dark side". This is a misnomer. The back of the moon gets the same amount of sunlight as the front. Unless you mean the side which is not presently illuminated. Water could freeze there but it would boil off again when the sun lights it up again.

However there are craters at the poles that never experience sunlight, and water does accumulate in them. You don't need any atmosphere to hold water vapor - the water vapor itself is held in the moon's gravity well and floats around until it cools somewhere, such as these craters.

>The back of the moon gets the same amount of sunlight as the front.

silly me, yes even better then, since in theory there should always be some amount of water vapor floating around? I just recall a weather phenomenon in Finland when the atmospheric temperature drops sufficiently that even the water vapor freezes and falls like 'stardust'. So would a big sun shield on the moon create a similar temperature drop allowing capture the ice crystals? maybe the moons gravity is insufficient.

> The back of the moon gets the same amount of sunlight as the front.

Actually, doesn't the back get more sunlight? The front of the moon is occasionally eclipsed by earth.

Why does the water vapor gravitate to the poles?

Also, if there is X amount of water, and ever thaw / freeze cycle loses some amount Y, can't we estimate what X was Z years ago?

It doesn't really gravitate to the poles, it's just that once water reaches a permanently shadowed bit of a crater, it stays there forever.

> Reminder that the moon does not have a "dark side". This is a misnomer.

It isn't. The side of the moon that cannot be seen from Earth is called the dark side of the moon. It's called that for the same reason that the Dark Ages are called dark: because we can't see them.

It is true that the dark side of the moon gets just as much sunlight as the light side does.

AFAIK the "Dark Ages" are named like that because the Renaissance people thought they were enlightened, compared to the "barbaric people" who lived before them, not because we have less documents (although we do)

Perhaps originally, but the reason it persists as a term even when used by people who don't think medieval people were relatively unenlightened is that it can also be construed as referring to the lack of documents. (And for those who do regard medieval people as relatively unelightened, they might regard the lack of documents as something intrinsically associated with that.)

I work in aerospace (lunar exploration actually), and everyone involved goes out of their way to always use the term far side and explain to laypeople about it. Regardless of its origin, I've commented on it in conversation at least a dozen times and I don't think I've yet had the other person use the phrase and not also think there is a permanently dark side of the moon.

Online there is often also some pedant who explains "well actually there is a dark side but it changes". Because your last sentence is about sunlight I actually interpreted "dark side of the moon" as the unlit/ lunar nighttime side on the first several reads.

Anyway it can be interpreted at least three ways:

- Referring incorrectly to the far side

- Referring correctly to the far side because actually dark means something else (but it will be interpreted incorrectly anyway)

- Referring to the side currently in lunar nighttime

The terms "near side", "far side", "lunar night" and "lunar day" are much better.

Sounds like something a person living on the dark side of the Earth would say.

The context was thermal energy received from the sun, not attention received from man.

Your clap-back might make sense when somebody is criticizing Pink Floyd, but it doesn't make sense here.

The current consensus is that any water deposited by a meteorite will be vaporized and lost unless it happens to end up in a "cold trap" permanently shadowed area. What you described is close to what happens when a meteorite with water hits the surface -water is dispersed and whatever water molecules randomly end up in a cold trap stay there.

Evidence of water in sunlit areas as in the article is new and it's thought that it is trapped in glass, so I think it's a separate mechanism and water escaping from inside of glass, being evaporated and then also ending up in a cold trap must be very unlikely.

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