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From pictures taken on the moon, it appears that there are no stars visible in the sky, but I do not know if this is an effect due to cameras.

  1. What is the actual appearance of the sky on the moon?
  2. Are stars visible?
  3. Is there any difference between the daytime and nighttime sky on the moon (other than the sun’s absence)?
  4. When the sun sets, does the surface of the moon instantly become completely dark?
  5. Similarly, when the sun sets, would the environment instantly become pitch black?
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    $\begingroup$ I hope that we get night time pictures by the new Indian moon rover to be absolutely sure about it. $\endgroup$ Sep 1, 2023 at 13:42
  • $\begingroup$ That is a lot of questions. $\endgroup$ Sep 2, 2023 at 21:20

3 Answers 3

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Quote from Buzz Aldrin:

“Obviously, when we touched down on the moon, we were very relieved. The immediate surface was very powdery, as best we could see looking down from 15 feet. Off in the distance was a very clear horizon, maybe with a boulder. And, of course, the brightness of the sunlit surface was almost like looking out at sunlit snow. Your pupils close down, just as in orbit when the sun is on the spacecraft. The sky is black as can be, but there’s no way you can see stars. They’re there, of course, but you can’t make them out because they’re too faint with all the ambient light in your eyes. I was impressed with the total “magnificent” desolation I saw in front of me: black sky, no stars and the horizon clearly curving away.”

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    $\begingroup$ Whereas you should probably see them much better than from earth, when you land on the night side of the moon, since there's no atmosphere. This answer does not yet address all points of OP $\endgroup$ Sep 1, 2023 at 13:40
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    $\begingroup$ (((remark about answers that are only quotes without any input from the creator of said answer))). - - - And then I noticed this was physics.se $\endgroup$ Sep 1, 2023 at 17:02
  • $\begingroup$ I wish I had some personal experience to complement what Buzz Aldrin said. :) To tell the truth I tried to find a video of a simulation in Stellarium that would cover more of the question. I didn't find anything good. $\endgroup$ Sep 2, 2023 at 16:11
  • $\begingroup$ @ThomasWeller, maybe. The astronaut would be seeing the dark sky through a curved sheet of transparent material (helmet), which could result in quite the diffusion and distortion. We might not know until someone tries it. Has anybody done an EVA while in the Earth’s shadow? Probably not, for safety reasons. That would be very similar, maybe even better (no scratches on the visor from moon dust to contend with) $\endgroup$ Sep 3, 2023 at 6:46
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That's because those photos are showing the black backdrop of the studio where they were taken...kidding.

The stars are not visible on the Moon, at least in photos, because the lunar surface in sunlight was so bright that the stars were washed out. No camera (nor the human eye, usually) has the dynamic range to process something very bright next to something less bright. If the aperture were open wide enough and the exposure long enough to collect enough light to image the dim source, it would collect so much light from the bright source in that time that this latter light would overpower everything else, and you would not get a comprehensible image. Try to take a picture of a candle flame with the mid-day Sun in the background.

As for human eyes, astronaut testimony may confirm stars were visible on the Moon when looking away from the surface. I do not have that information. I tend to think if a camera were pointing straight at the sky with "blinders" on to block surface light, you would see the stars just as well as in empty space.

The thing to remember on the Moon is, the lack of atmosphere means there is no refraction or scattering of light. The only light you see in any direction is the light that came from that direction. If the Sun is in your field of view, you see it. If you turn your back to it, the sky is as dark as night. Anywhere around the Sun is also as dark as night (though you may not see stars, as mentioned before). When the Sun sets, its light immediately disappears, though you would still have light from the Earth, so it may not be pitch black, but would be much darker.

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    $\begingroup$ You can compare an Earthlit sky on the moon to a moonlit sky on Earth. Note that the Earth is larger than the Moon, and that the Earth is substantially covered in white clouds, so the Earth will be substantially brighter than the Moon. Earth will go through phases (crescent, gibbous, full, gibbous, crescent) as senn from the Moon, but will not rise or set, because the Moon's "day" has the same length as the month. $\endgroup$
    – rob
    Aug 31, 2023 at 4:03
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    $\begingroup$ @Peter-ReinstateMonica Whoops, yes. I was thinking of the illumination of the Moon's surface: a full Moon is bright enough to cast obvious shadows and to read surprisingly fine print. But I wrote "sky" instead out of habit. $\endgroup$
    – rob
    Aug 31, 2023 at 13:31
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    $\begingroup$ @rob More than just clouds (but they are important): the moon is grey rock with an albedo of 0.12, worn asphalt. The Earth is 0.3! In total, the Earth is 34x brighter than the Moon (on the other surface). The Earth on the thinnest (not completely gone) day of its 28 day cycle is about as bright as a full moon. $\endgroup$
    – Yakk
    Aug 31, 2023 at 13:54
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    $\begingroup$ @SolomonSlow As another comment has pointed out, the Sun's corona will be visible for some time after the Sun's disk has disappeared below the horizon. The entire corona, as visible from Earth during an eclipse, is about as bright as a full Moon (viewed from Earth). Discussions about observing "Bailey's beads" during a solar eclipse on Earth give some inkling of the experience of watching the Sun disappear below the lunar horizon. $\endgroup$
    – rob
    Sep 1, 2023 at 4:19
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    $\begingroup$ Gene Cernan said that, while standing in the shadow of the Apollo 17 LM, he could see some stars while he was outside. $\endgroup$
    – Hobbes
    Sep 1, 2023 at 17:57
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It was daytime

This was a deliberate choice by the mission planners to avoid the obvious problems of landing at night i.e. it’s dark at night time.

The reason you can’t see stars on the Moon during the daytime is the same reason you can’t see them on Earth, your eye is adapted to the average luminance in your field of view.

The day lit Moon’s surface has a more or less constant luminance of about 2.5 kcd/m2 the Earth varies depending on cloud conditions between about 0.7 and 5 kcd/m2. A moonlight night on Earth is about 1.4 mcd/m2 - note the k for kilo and the m for mili; we’re talking 6 orders of magnitude here.

The human eye is good, it can adapt to cover about 10 orders of magnitude: just not all at once. Once adapted, it can cover about 3 orders of magnitude. That means, for an eye adapted to look at the Moon or the Earth, the stars are just too dim.

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    $\begingroup$ Of course, at nighttime you can't land on the moon because it's pitch black and you might miss it. $\endgroup$
    – Richard
    Sep 2, 2023 at 8:00
  • $\begingroup$ What a great answer. $\endgroup$
    – Fattie
    Sep 2, 2023 at 19:52
  • $\begingroup$ It is fairly easy to see Venus during the day on this planet if you know where to look (and blocking out the Sun using a building (or if you have a spacecraft at hand...)). It ought to be even easier on the moon. Perhaps the helmet, with reflections, refractions, and filters were the real problem? $\endgroup$ Sep 2, 2023 at 21:27
  • $\begingroup$ @PeterMortensen Well, there's the thing... they weren't there to take pictures of the stars. We already had better pictures (and eyewitnesses) from Earth's orbit, and of course... the trip to the Moon. And I suspect they couldn't just look up in their space suits :D $\endgroup$
    – Luaan
    Sep 3, 2023 at 7:52

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