How Hot is it on the Moon?

I've broken this topic off from the thread titled, "Neil Armstrong: Why I Didn't Walk Far on Moon" because there seems to be a lot of misunderstanding on the subject.

Let's talk about the "temperature on the moon". That phrase has led to a lot of confusion. You have no doubt heard that the temperature on the Moon varies from -250F up to 250F. I live in Texas, and in the summertime, the temperature gets up over 100F, so standing on the Moon must be like standing in an oven, right?

No.

If, on a hot summer day here in Texas, I walk out on the sidewalk barefoot, it's hot enough to cause pain. If I step onto the asphalt street, I will blister my feet. Why? 100F is less than two degrees above normal body temperature. The solid pavement is hotter than the transparent air because it absorbs more radiant energy from the sunlight. The light-colored concrete sidewalk may heat-up to 120-140F. The darker asphalt may get up to 180F or more.

When we ask, "what is the temperature outside?" we are asking about the ambient temperature of the air. On the Moon, there is no air, so when we ask about the temperature there, we are asking about the temperature of a specific object on the surface; a patch of dirt, a rock, a camera or an astronaut's spacesuit (and specifying whether it is the side facing towards or away from the Sun). Note that this varies: In my above example, the sidewalk was ~130F, but the asphalt was 180+ F. When a textbook says that it gets up to 250F on the Moon, it is referring to the surface of a black, solid object with its face perpendicular to the Sun at local noon.

The actual lunar surface is not black: It's about the same shade as asphalt (not the fresh-laid black stuff, but rather the dark/medium grey color it fades to after a few years). It heats up to roughly 200F. Mind you, the Moon is the same average distance from the Sun as the Earth. All things being equal, lunar regolith and asphalt should reach the same temperature. However, the asphalt is cooled somewhat because the air in contact with the pavement conducts away some of the heat (we can see it doing this: it causes the shimmering effect when we look across a hot parking lot). Also, daylight only last ~12 hours on Earth, but it's 14 days from sunrise to sunset on the Moon.

I said before that the pavement here in Texas can get up to ~180F. However, on a summer day I can go outside and walk on it barefoot with no discomfort. How? It's simple: I do it at 8:00am, before it gets anywhere near that hot. The Apollo astronauts did the same thing: They landed when the rising sun was only ~10 degrees above the horizon and the surface temperature was ~30F. When they left three days later (on the longest missions), the sun was still only half-way up the sky, and the surface temperature was a bit over 100F (yes, NASA did have the technology to make insulated shoes in the 1960s ).

(Allow me to state the blindingly obvious: The surface starts out cold because it has spent all night radiating its heat into space. As someone else already pointed out, when a surface is in the sun, it absorbs light based on its reflectivity (more reflective absorbs less energy) and its angle to the sun (a perpendicular angle to the light absorbs more than an oblique angle). When the same surface is shaded from the sun, it radiates heat as efficiently as it absorbs it - a black surface radiates faster than a light one.)

For astronauts, heat management is a crucial issue that requires careful engineering, whether they are on the Moon or in Earth orbit - Remember, they are at the same average distance from the Sun. In fact, the Earth is more reflective than the Moon, so astronauts & spacecraft in Earth orbit get more reflected energy than those on the Moon (even though the surface is much further away, there's a lot more area doing the reflecting). For spacecraft & spacesuits (which can be thought of as mini-spacecraft), the engineering solution is basically the same: Keep as much of the outside heat out and control the heat that's being generated on the inside to maintain comfortable levels.

Outside heat from direct & reflected sunlight is kept out by using a reflective outer layer, backed up by layers of insulation. When you look at the flimsy-looking outer covers of the Lunar Module, you're only seeing the reflective skin that covers the actual structural members and pressure vessels beneath. Interestingly, Middle Eastern nomads developed the same principle centuries ago: Those volumous white robes they wear serve the same function, and work better than shorts and a t-shirt to keep them cool in the desert.

Inside, heat is generated by electronics and by the astronauts themselves. On full-size spacecraft, most of the heat comes from electronics, and any excess goes to shielded radiators on the hull (on Apollo 13, when they lost power, they shut down the electronics and therefore their main heat source, which is why it got so cold). Men doing geology on the Moon, and building the International Space Station in orbit are basically doing heavy work for hours in an airtight rubber suit. Beneath the rubber, they wear something like long underwear that has a whole network of tubes. They pump water through the tubes to something called a porous-plate sublimator, which carries the heat away to space.

The smaller pieces of equipment on the Moon, such as cameras and experiment packages mainly relied on reflective outer casings. In these cases, keeping the dark lunar dust off of them was a major concern. On the EVA videos, you can hear some exasperation from the astronauts after the umpteenth request from Houston to dust-off the TV camera because it's overheating. Of course, the astronauts and the still cameras they carried were almost constantly turning this way and that, so individual surfaces spent as much time facing away from the Sun as towards it.

Hopefully this helps clear things up.

too bad half of them lied about hes travelling distance on the moon, not to mention that it might be a hoax because the flag was moving like there was wind on the moon + a whole lot of other conspiracies. but thankyou for your info

I understand there is actually a thin layer of atmosphere on the Moon. Also it's color is more like rusty brown.

Look :

[atsimg]http://files.abovetopsecret.com/images/member/6cb8e50ad7ae.jpg[/atsimg]

With compliments to Nasa and Phage for giving me the link. in this thread I once made.

Very interesting thread by the way. I never thought about like that. S & F

As I was one the members confused in the other thread your noted, I just want to say Thank You. You provided a clear, understandable explanation of the temperature, and why it changes (the factors and variations) on the lunar service. I appreciate the analogy to Texas as well. S&F from me as well.

WOW, that was a very clear explanation! Even I understood it and sometimes you have to get to the level of Sesame Street for that to happen!!!! Hah!

Thank you very much for taking the time to explain it

Originally posted by SkYSLeePeR001
too bad half of them lied about hes travelling distance on the moon...

No they aren't.

...not to mention that it might be a hoax because the flag was moving like there was wind on the moon...

No it wasn't.

... + a whole lot of other conspiracies...

...that don't hold-up under examination.

...but thankyou for your info

You're quite welcome. I recommend www.clavius.org. It will answer many of your questions.

Originally posted by Sinter Klaas
I understand there is actually a thin layer of atmosphere on the Moon. Also it's color is more like rusty brown

The moon's so-called atmosphere is so thin that it's a better vacuum than you can get in many labs on Earth. You could compress the entire lunar atmosphere into less than two hundred 300psi diving cylinders.

The colors in your [lovely] picture are very exagerated. To the eye, the moon looks like... like... well, just like it does to the eye - basically grey. By exagerating the colors, they can get valuable information about differences in composition. You're partly right though - The astronauts who went there found that, from certain combinations of lighting and viewing angles, the normally grey volcanic surface took on a goldish-brown cast. Weird...

Originally posted by Saint Exupery
The moon's so-called atmosphere is so thin that it's a better vacuum than you can get in many labs on Earth. You could compress the entire lunar atmosphere into less than two hundred 300psi diving cylinders.

Did you by any chance mean 3000 psi? That would be more along the lines of a typical diving tank pressure at the start of a dive, is why I ask. I tried searching for that statistic a little but I didn't find it, but I know the atmosphere on the moon is practically nonexistent. There are so few molecules there that when Apollo did the orbital insertion burns, the rocket exhaust contributed significantly to the moon's atmosphere:

www.telegraphindia.com...

A 1991 publication on lunar science, The Lunar Sourcebook, had pointed out that the lunar surface has been observed to change with human presence. Human effects on the near-vacuum of the lunar atmosphere are “potentially worrisome”, planetary scientists had written.

Each Apollo mission released on the moon a mass of gas roughly equivalent to the existing lunar atmosphere, they had pointed out.

“The gases from the Apollo landing module and those escaping from (the astronauts’) space suits doubled the lunar atmosphere,” Grant Heiken, a geologist who had worked with Nasa during the Apollo programme and had contributed to the 1991 sourcebook, told The Telegraph.

It has been assumed all along, Sridharan said, that the lunar atmosphere would return to its original state within a few months as the gas molecules will be ejected into space. “But we need to keep our minds open,” he said.

I'm not sure if it did return to it's original state within a few months though. But the point is, it that small Apollo mission doubles the moon's atmosphere, there's not much there.

Great thread to clarify a poorly understood concept! Temperature is understood in context of the Earth's atmosphere but most people don't understand it outside the Earth's atmosphere. You did a great job of explaining it!

It's very strange that in interstellar space it can be a million degrees and you can still freeze to death. That's because there are so few of those million degree molecules hitting you that they don't really warm you up much at all, so you radiate all your heat away and freeze! In a million degree temperature space!

To warm you up, you not holy have to have a high enough temperature of the molecules hitting you, but there have to be enough of them (adequate density) to have an effect. Interstallar Temperatures and densities

Temperature can become somewhat unintuitive once we leave the confines of Earth.

So if you are in space, and you are facing the sun (a sun) and half of your surface area is exposed to the sun at more less a perpendicular angle, you won't warm up unless there are particles already in space that are then hitting you, for example atmosphere, for you to absorb their temperature. Hence freezing in the next to nil atmosphere of the moon. Now, if I am interpreting this correctly, and the info is correct, then why the reflective layer on all space craft and space suits. I understand it's to absorb a minimal amount of radiation, but won't the adsorbed energy from the radiation warm things up?

I'm kind of talking this out in my head, because what was said would make sense in the shade where there is nothing (no atm) to retain the absorbed energy (heat).

you are absolutely wrong - and in more ways than one - but here is one: When an object is facing the sun - at any angle...it will heat up quickly....quicker than on earth where you have 100 km of air shielding you...this heating process is QUICK...however...Put that heated object behind something so it is now shaded from direct sunlight and it will have NO-WHERE to exchange its heat to - it will cool down eventually through its own atoms slowing down...but this will be a lifetime....And I mean it will take a lifetime to cool once it is heated...Its like a one way gate - its easy to get heated but impossible to shed that heat once attained....you are misled by the word "sunlight" it sounds such a pretty word but outside our air barrier that sunlight becomes a superheated all engrossing stream of nuclear rays and particles...the surface of the moon that has the sun on it(which does change slowly) is such an unprotected object....!this is just one of your obvious errors...Is this your occupation - espousing impossible theories to placate an impossible lie...
You have been personally addressed by General Hercules - YOU SHOULD TAKE NOTE

[What do you mean " the astronauts who went there" no astronaut has been higher than 250 kilometres let alone gone to the moon - You've been left tbehind by a cruel world....its scary to think what other lies of the planet you have swallowed...there is one other possibility....maybe this is your job....If so go and tell your employer that you have been persally found out by the General Hercules....and this a reason for you to be concerned

Originally posted by ProDidgewwo
So if you are in space, and you are facing the sun (a sun) and half of your surface area is exposed to the sun at more less a perpendicular angle, you won't warm up unless there are particles already in space that are then hitting you, for example atmosphere, for you to absorb their temperature. Hence freezing in the next to nil atmosphere of the moon.

You won't freeze to death in stellar space, like around the Earth and moon, but you will in interstellar space where there's no significant sunlight, all you get is starlight in interstellar space.

The electromagnetic radiation from the sun is plenty to keep you warm in space, as someone said it's blasting you with 1500 watts per square meter, so like a 1500W space heater hitting your suit. The EM radiation and particles are two different things, the temperature of the particles in space alone won't keep you warm, you need the EM radiation of the sun for that.

Originally posted by Unionoffreehumans
And I mean it will take a lifetime to cool once it is heated...Its like a one way gate - its easy to get heated but impossible to shed that heat once attained.

Why do you think it's so hard to shed heat quickly?

Even on the Earth, deserts are known to shed heat quickly and go from hot in the day to cold at night and they have the atmosphere for a buffer. In space you can radiate heat even more quickly on the shaded side.

This uneven heat is why they rotated the spacecraft:

science.howstuffworks.com...

In outer space, the difference in temperature between sunlight and shade is about 400 degrees Fahrenheit. This uneven heating causes thermal stress on the metals in the spacecraft's structure. To counter this effect, the Apollo spacecraft rotated on its axis when going to the moon to allow solar radiation to heat the spacecraft evenly (the "barbecue roll maneuver").

I like that name: "barbecue roll maneuver"

Thank You for this thread
I never realized what you said, I should have guessed it as everyone else

Brilliant Thread

reply to post by Sinter Klaas


O, I think you'll find that the color present in that particular image is from an "enhancement" done, to the photo itself. A form of "false color". Is seen in many examples, for various reasons.

I think the intent, there, is to show the general "colors" of the various areas, IF you get get up close. And view it without the surrounding glare, for other areas. Something like that. It's like, you back away from the Earth far enough, and it all blends into a pale whitish-blue...but come back closer, and out pick out distinct colors, land versus ocean, versus desert versus rain-forest, etc.

But no.....there isn't anything like an "atmosphere" to alter the perception of the Moon's colors. It's a matter of distance, relative brightness, and perspective. AND, what is doing the imaging. Our eyes see differently than many of our machines, for example. We can alter the resulting photos to our taste....like how you can alter the color adjustments on your TV screen display.

I think that lunar regolith is white (like concrete) since it reflects many different wavelengths in the optical spectrum. At 1600 watts per square meter of incident radiation on the moon, compared to the atmosphere scattered radiation on Earth which is only about 100 watts per square meter near the equator at noon (give or take depending on cloud cover and seasonal variation in orbital distances as well as fluctuating hydrostatic atmospheric heights), the white regolith heats up a lot more than even the blackest asphalt roads on Earth.

Originally posted by Sinter Klaas
I understand there is actually a thin layer of atmosphere on the Moon.

It's a virtual vacuum. Just about every astronomical body with a bit of gravity will have an "atmosphere" so-to-speak, caused by dust being kicked off the surface by micro-meteors and by out-gassing of the soil.

But that extremely tenuous atmosphere on the Moon is still virtually a vacuum.

Also it's color is more like rusty brown.

I suppose I should get my telescope fixed. The Moon looks gray through that damned thing.
Stupid telescope.

Originally posted by Soylent Green Is People
But that extremely tenuous atmosphere on the Moon is still virtually a vacuum.

Indeed it is.

I suppose I should get my telescope fixed. The Moon looks gray through that damned thing.
Stupid telescope.

Did you ever try processing the image taken through a telescope? It does produce interesting results:
blog.deepskycolors.com...

Is the moon really like this? Well, sort of. This is what happens when you take a picture of the moon, neutralize the colors (so the median of the values of R, G and B is the same) and then saturate the image. So in a way, yes, those colors are real, and the only difference is that they've been exaggerated a bit.
Imaging Scope: Televue NP101is + Powermate x4

The astronauts apparently did see a little color on the moon, but it may have looked tan from one angle and gray from another. They also reported seeing some of the colors in that enhanced image.

Also note the astronauts said the Earth colors looked less vivid from a distance, so I'm not surprised we can't see the color tones of the moon from Earth, but the camera does pick up some color variation as this photo shows when the variation is magnified.

Originally posted by quantum_flux
I think that lunar regolith is white (like concrete) since it reflects many different wavelengths in the optical spectrum.

Actually, it's quite dark. It only looks bright in the night sky because of the contrast between space (as seen by our dark-adapted eyes) and the sunlit lunar surface. If you look at the Moon in the daytime and compare it to sunlit concrete on Earth, you will readily see that the regolith is darker. In fact, the albedo (reflectivity) of the regolith varies between 7% in the dark, basalt maria and 12% in the breccia-laden highlands. You are correct, though, that its reflectivity is fairly constant across the visible spectrum.

Originally posted by quantum_flux
At 1600 watts per square meter of incident radiation on the moon, compared to the atmosphere scattered radiation on Earth which is only about 100 watts per square meter near the equator at noon...

These numbers are not correct. For starters, the solar constant is ~1400 Watts per square meter (source - Remember that the Moon, being at the same average distance from the Sun as the Earth is, receives the same solar flux as the Earth). Furthermore, if the flux at the Earth's surface was 100 W/m^2, then that would mean that only 1/16 (using your number) or 1/14 (using mine) of the energy was making it through the atmosphere without being absorbed or scattered. We can readily see this is not correct by performing a simple experiment (no special equipment required):

If we look straight-up from the surface of the Earth, we are looking through "one thickness" of the Earth's atmosphere. If we look at the sky at a slant (non-vertical) angle, we are looking through a greater thickness of the Earth's atmosphere. Using a little trig, we find that if we look up at ~30 degrees (1/3 of the way from the horizon to straight overhead), we are looking through "two thicknesses" of the Earth's atmosphere.

Thus, the difference in atmospheric effects from 30 degrees to 90 degrees is the same as the difference between looking at 90 degrees through the atmosphere and looking through no atmosphere at all.

So if the atmosphere were absorbing/scattering more than 90% of the incoming light (as your numbers suggest), then the Sun, Moon and stars would be more than 10 times as bright when straight-up as compared to when they are one-third of the way to the zenith. We can see with our own unaided that this is not the case. In fact, we can see that objects straight-up are less than twice as bright, therefore we know the atmosphere absorbs/scatters less than 50% of incoming light. Depending on the conditions (which you correctly enumerated), the solar flux at the ground is roughly 1000 W/m^2.

Perhaps you were thinking of the power obtained through conversion of solar energy. Most conversion systems are only ~10% efficient, so if you had a 1000 W/m^2 flux, then you would only get 100 Watts per square meter of 10% efficient solar panels.

Originally posted by Saint Exupery

Originally posted by quantum_flux
I think that lunar regolith is white (like concrete) since it reflects many different wavelengths in the optical spectrum.

Actually, it's quite dark. It only looks bright in the night sky because of the contrast between space (as seen by our dark-adapted eyes) and the sunlit lunar surface. If you look at the Moon in the daytime and compare it to sunlit concrete on Earth, you will readily see that the regolith is darker. In fact, the albedo (reflectivity) of the regolith varies between 7% in the dark, basalt maria and 12% in the breccia-laden highlands. You are correct, though, that its reflectivity is fairly constant across the visible spectrum.

Pardon the thread necromancy, but I just found this cool video that demonstrates the difference in albedo between the Earth and Moon. At 00:16 seconds you can see the sunlit side of the Moon superimposed on the Sahara Desert. The lunar regolith is much darker: