Why are there no stars visible in cislunar space?

Question

It’s very puzzling that the moon landing had no stars in the background, the ISS clips have no stars in the background. I listened to multiple astronaut interviews speak on what it looks like up in space and about half of them speak of the “darkest black space”. I’m sure there is a very good explanation for this.

Is star light only visible through the medium of earth atmosphere? But once in the vacuum of space where there is no medium they disappear? What’s the explanation?

Minute 47-49 stars, press conference all three Apollo 11 astronauts

BBC interview with Neil Armstrong only

Answer 1

It is a matter of exposure and dynamic range. A sensor like a camera can only handle inputs in a certain range of intensities, and much of photographic skill (or smart presets) is about mapping the outside light onto this range so the details you care about show up rather than turn into white or black.

If you take a picture of a brightly lit scene, in order to make out the details of the bright parts (such as a lunar landscape, the Earth, the ISS etc) you will have to adjust the exposure making faint objects like the stars too dim to see against a dark sky background. You could try to set the exposure to show the stars instead, but now the landscape and Earth would be too bright (and likely also mess up the picture by causing flaring).

One can try to work around it by taking several pictures at different exposure levels and later digitally compositing them together. But this requires a lot of extra work.

Answer 2

Anders's answer is entirely fine, but I'd like to add some extra information. As evidenced by the transcripts, reflected Earth light is quite strong even at this distance:

The earthshine coming through the window is so bright you can read a book by it.

That is, even with the lights turned off, it would probably be tricky to see the stars unless you turned in a way that didn't allow the earthshine through the windows.

However, as the capsule comes into the shadow cast by the Moon (a pure accident - they didn't plan for the approach to go this way), there comes:

Houston, it's been a real change for us. Now we are able to see stars again and recognize constellations for the first time on the trip. It's - the sky is full of stars. Just like the nightside of Earth. But all the way here, we have only been able to see stars occasionally and perhaps through the monocular, but not recognize any star patterns.

So for a few minutes, they did see "the sky full of stars". Other than that, they've seen a few stars once in a while, but only singular, bright stars (perhaps also when looking in a way that minimized the brightness from the Earth and Sun):

Houston, it's been a real change for us. Now we are able to see stars again and recognize constellations for the first time on the trip. It's - the sky is full of stars. Just like the nightside of Earth. But all the way here, we have only been able to see stars occasionally and perhaps through the monocular, but not recognize any star patterns.

The core of Anders's answer is still true, though. Exposure is the main problem here - both cameras and human eyes have a certain dynamic range, and even the brightest stars are entirely too dim in comparison with both the Sun, the Earth (in distance comparable to the Moon's distance from the Earth) and the Lunar surface (if you're in sunshine, as most of the mission was). A modern camera might be able to take a HDR picture that would allow the stars to be visible at the same time as the Earth or the Sun, and it'd be quite easy to do if you could occlude the main light sources (the same way we do it when photographing the Sun's corona etc.). But technically, that would be a "doctored" image - taken at two different exposures and combined in a way that uses different exposures for different parts of the image.

Answer 3

The reason is that:

1. To take a photograph under different lighting conditions, you need to use different camera settings to get a useful image.
2. Cameras (and the human eye) do not have unlimited range in any given set of conditions, that is, they cannot represent objects of every brightness satisfactorily within one single image.

In particular, if one is photographing a subject that is brightly illuminated, one has to use camera settings that greatly limit the amount of light being recorded by the camera's sensor, otherwise it will be overwhelmed and fail to show useful detail. In the case of taking a subject that is only dimly illuminated (or, in this case, emitting only what amounts to a dim light), such as the stars, one needs to use settings which maximize the amount of light that the sensor absorbs to get useful detail in the image, or one will record nothing. These two types of settings are logically incompatible, and thus it is impossible (with existing camera technology) to capture simultaneously a very dim and very bright subject in a single (i.e. not a composite) photograph and have both of them look sensible.

And the Moon and stars are just such an incompatible pair. The Moon's surface is lit up effectively as brightly as the landscape of Earth in broad daylight. The stars are so dim they can only be seen at night.

In fact, you can demonstrate this right from Earth itself. Here are two photographs I took with my own camera about ten megaseconds or so ago, as of this posting. Both were shot at night, on the same night. The left hand photograph is shot with the camera set to daylight settings. Yes, these are the same settings you'd use to shoot a photograph in actual daylight, only being used at night, and the Moon registers loud and clear. That is how bright it is. Since surface brightness is not affected by distance, the Moon effectively amounts to a little piece of sunlit landscape in the sky, from our point of view, just like on a bright, sunny day on Earth. As you can see, the Moon's surface features are cleanly visible and, moreover, it is similar in coloration to your last photograph - as it should be, because that is its actual color. Note the complete absence of stars, exactly as in the NASA images. In the second photograph on the right, the camera was set to "bulb" mode to expose the sensor for a long time, and its sensitivity was greatly increased. You can now see the stars, but the Moon looks almost like a second Sun - its surface features completely obliterated as the sensor has been saturated with photons like a sponge that has already soaked up too much water and has now had enough, while bloom contaminates the rest of the image. The reason you "expect" to see stars is likely because you have watched too many sci-fi movies. Movies depict stars for artistic effect. In reality, images capturing such, taken in a single bout, are not possible with today's tech, and the reason is that the factor between the two is on the order of a billion (90 dB) in brightness. (You could composite the above two images suitably to fake it, but it would be just that.)