Observing from the Moon?

[stem1989]

Sorry, I'll have to correct you here, there is no dark side of the Moon, only Far Side of the Moon, which receives on average exactly the same amount of sunlight as the Near Side. The trick would be to go to the bottom of a very deep crater that is permanently shaded, and observe there all day, every day.

Would need me finest wooly hat, scarf and gloves for that... sounds a bit chilly

[Knight of Clear Skies]

Guess it might be a little chilly though, perhaps long johns would be needed, or am I forgetting something???

Actually, the problem on the moon is to keep cool, even on the nightside. The ambient temperature there may be very low, but there is no atmosphere. On Earth, body heat is dissipated primarily through convection with the air around us and evaporation of sweat. On the moon, it can only be removed by radiation or though contact with the ground. Spacesuits have to be fitted with cooling systems.

It's very unintuitive. Space is mostly very cold, with some regions that are very hot; but unless you are close to a star and absorbing radiated energy it would make very little difference to a human. For example, gases in a nebula can be between 8,000 and 23,000 C, but the density is so low you wouldn't really notice.

[Naemeth]

Actually, the problem on the moon is to keep cool, even on the nightside. The ambient temperature there may be very low, but there is no atmosphere. On Earth, body heat is dissipated primarily through convection with the air around us and evaporation of sweat. On the moon, it can only be removed by radiation or though contact with the ground. Spacesuits have to be fitted with cooling systems.

It's very unintuitive. Space is mostly very cold, with some regions that are very hot; but unless you are close to a star and absorbing radiated energy it would make very little difference to a human. For example, gases in a nebula can be between 8,000 and 23,000 C, but the density is so low you wouldn't really notice.

Not if you are in an area of permanent shade. If you are there, ice freezes pretty much as hard as rock, keeping warm (but not too warm) would be the issue in that case. As soon as you move into sunlight however...

[Knight of Clear Skies]

Not if you are in an area of permanent shade. If you are there, ice freezes pretty much as hard as rock, keeping warm (but not too warm) would be the issue in that case. As soon as you move into sunlight however...

Even there, keeping cool would be the problem, as only your feet would be in contact with the ground. It's not practical to keep your body cool just through your feet, your boots would need to be well insulated to prevent frostbite. You could crudely regulate your temperature by lying down briefly every now and again.

Like I say, it's very unintuitive, because it's an environment very different from what we are used to.

[Zakalwe]

The only reason that you'd heat up in a suit is because a suit is thermally very insulating (many layers of fabric, a rubber pressure bladder and so on).

Anything left on the Moon, exposed to the blackness of space, very rapidly radiates it's heat away (there's no air layer to insulate it). Apollo astronaut John Young learned this painful lesson when he collected a large rock. He placed in the LM's shadow where it radiated it's heat away quickly. When he re-pressurised the cabin he tried to move the rock to balance the ascent stage and promptly found that the rock was bitterly cold. He was lucky not to suffer frostbite.

An object in an vacuum, exposed to the perfect black-body absorber that is space, will very rapidly dump it's heat load. It doesn't have any atmosphere to insulate it and to slow it's radiative heat loss.

[Knight of Clear Skies]

The difference between a human and a rock is that the former has a built in heater. Even at rest, the average person generates about 60 watts, much more when they are active. If this is more than can be radiated through the suit - no matter how thin it is - and conducted through the soles of their boots, the person will warm up. I'm fairly sure a human can't radiate 60 watts through their skin. If they did, you could point a solar panel at them harvest a few watts of power off them.

I'd welcome an actual figure for how much body heat is lost through radiation as opposed to convection and evaporation of sweat.

As for that moon rock in the LM's shadow, did it lose most of its heat through radiation, or conduction against the cold moon surface? Vacuum is a perfect insulator, which is why vacuum flasks are so good at keeping liquids hot or cold. (As the joke goes, how does it know, Jim?)

[Knight of Clear Skies]

I found a short article here which tries to explain this, hope it is of some help. The "space is cold" meme is deeply embedded, and the reality is very counter-intuitive.

"When we think about heat we think about a form of energy. However we forget that heat like most forms of energy such as sound needs a medium to travel through. In the case of heat it needs matter to conduct it. A piece of forged iron when quenched transfers its thermal energy to the liquid that quenches it. If you place a plate of heated food out on a table for a long period of time the process of convection transfers the heat from the food to the air molecules surrounding it. In space the rules differ. A perfect vacuum has no molecules to transfer heat to. This means it can’t properly conduct heat. This principle is used to store hot liquids in storage containers such as thermoses. Essentially even though you may think of space as cold it would actually allow hot objects to retain heat longer than if they were on Earth...."

Also, please bear in mind: all spacesuits have cooling system, but typically they only have heaters in the gloves, which are used to handle other objects. And even if the astronaut is in sunshine, half of them is in their own shadow. The difference in temperature between the front and back of the suit can be 135 C.

[Zakalwe]

I guess that its all a bit of a moot debate as you'd need a space suit and such suits are, by the nature of their construction, very very insulating. So without active cooling you'd quickly start to stew in your own juices as Gene Cernan found out in his Gemini EVA.

I'd welcome an actual figure for how much body heat is lost through radiation as opposed to convection and evaporation of sweat.

There's a fair few technical documents over on the Nasa Technical Reports Server with details on suit cooling. They might contain the amount of heat lost through radiation (I did find one web article that mentioned up to 65%). These two caught my eye:

http://ntrs.nasa.gov/archive/nasa/casi.ntrs.nasa.gov/19680017229_1968017229.pdf

http://ntrs.nasa.gov/archive/nasa/casi.ntrs.nasa.gov/19740006733_1974006733.pdf

As for that moon rock in the LM's shadow, did it lose most of its heat through radiation, or conduction against the cold moon surface? Vacuum is a perfect insulator, which is why vacuum flasks are so good at keeping liquids hot or cold. (As the joke goes, how does it know, Jim?)

Sorry, I don't know that.

[Zakalwe]

Vacuum is a perfect insulator, which is why vacuum flasks are so good at keeping liquids hot or cold.

No, that's not correct at all. The vacuum in a Dewar flask prevents heat loss by conduction and convection. Heat loss by radiation is reduced by silvering the insides of the flask wall to reflect heat back into the contents. If vacuum is a perfect insulator then how does the Sun's heat reach us?

[Knight of Clear Skies]

No, that's not correct at all. The vacuum in a Dewar flask prevents heat loss by conduction and convection. Heat loss by radiation is reduced by silvering the insides of the flask wall to reflect heat back into the contents. If vacuum is a perfect insulator then how does the Sun's heat reach us?

Sorry, I'm being a bit loose with terminology here. Vacuum is a perfect insulator as fas as conduction and convection is concerned. Obviously, it doesn't block radiation at all.

However, like I say, the human body dissipates most of its heat through convection and by sweating. So if you take that away by placing them in a vacuum, their heat will rise.

I guess that its all a bit of a moot debate as you'd need a space suit and such suits are, by the nature of their construction, very very insulating. So without active cooling you'd quickly start to stew in your own juices as Gene Cernan found out in his Gemini EVA.

No, this can be worked out, the physics is understood. This is how the suits were designed in the first place - with cooling systems, not heaters.

[Zakalwe]

This is how the suits were designed in the first place - with cooling systems, not heaters.

The first suits were developments of pressure suits worn by high-altitude pilots and had little or no cooling. The Gemini EVA suits (there were, IIRC, 3 different type of Gemini suits) had some limited air cooling, but Cernan's extreme difficulties showed that this was no-where near good enough (at the time there were concerns that he was going to pass out or cardiac arrest due to the heat stress that he was under). As a result, the water cooled undergarment was developed, which was used in the Apollo missions.

[Knight of Clear Skies]

The first suits were developments of pressure suits worn by high-altitude pilots and had little or no cooling. The Gemini EVA suits (there were, IIRC, 3 different type of Gemini suits) had some limited air cooling, but Cernan's extreme difficulties showed that this was no-where near good enough (at the time there were concerns that he was going to pass out or cardiac arrest due to the heat stress that he was under). As a result, the water cooled undergarment was developed, which was used in the Apollo missions.

I see, that's interesting. Either they got their maths wrong, or underestimated how active he'd be on the spacewalk and how quickly he'd warm up. Doesn't change the fact, cooling is required.

[Zakalwe]

I see, that's interesting. Either they got their maths wrong, or underestimated how active he'd be on the spacewalk and how quickly he'd warm up.

I think that's what happened. Ed White's first EVA didn't show such concerns, for probably a couple of reasons: White was superbly fit and he didn't do much else other than float about. Cernan had to manoeuvring himself to the rear of the craft to get the EMU. The Gemini didn't have hand or footholds and the effort of trying to hold himself in position, strain against the stiff pressurised suit and move was just too much. Aldrin practised extensively in the water tank and worked on hand and foot holds for the later Gemini. That, along with a water cooled garment meant that he had no problems with over-heating.

[101nut]

An example of how hot it is on the moon - Charlie Duke, on the Apollo 16 mission, left a photo of his family on the moon by simply dropping it onto the surface ... where he watched it shrivel with the heat!

AndyG

[ArmyAirForce]

....left a photo of his family ..... where he watched it shrivel with the heat!

AndyG

Really?? The NASA website states "Charlie put a picture of the Duke family - Charlie, Dotty, and sons Charles and Tom - on the surface and took several pictures of it."

I don't see any mention of the photo degrading, just that he took several pictures.

http://www.hq.nasa.gov/office/pao/History/alsj/a16/AS16-117-18841.jpg

from this page - http://www.hq.nasa.gov/office/pao/History/alsj/a16/images16.html#18104

[spurius]

Considering the stars are light years away, you would have to travel way out of our solar system to noticeably move them from our current line of sight.

Like all the planets, the moon DOES have a dark side. On some occasions you can actually see it. The side of the moon facing earth is only part lit (crescent, half moon etc)but you can still see the rest of it. Apparently thats the sunlight reflecting off earth and lighting up part of the moon that isnt in direct sunlight. People must be confusing dark side with the far side which we cant see. Im a dumbass so confirmation from someone else is needed to back up this statement.