The title says it all. Why did the astronauts leave a mirror but not a camera on the Moon? Also, is there a reason why the Hubble telescope was built to orbit the Earth and not built to be on the Moon?

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    $\begingroup$ They did leave a camera on the moon. It took video of the LEM taking off. youtu.be/sj6a0Wrrh1g?t=169 $\endgroup$ Jul 22 '21 at 15:37
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    $\begingroup$ @PcMan You had a nice answer. Why did you delete it? $\endgroup$ Jul 22 '21 at 17:12
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    $\begingroup$ Are you referring to the LLR retroreflectors? And I think the Hubble question should be a separate question. $\endgroup$ Jul 22 '21 at 17:27
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    $\begingroup$ Your question about a telescope on the moon has an answer here $\endgroup$ Jul 22 '21 at 19:52
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    $\begingroup$ I agree these are two unrelated questions and should not be posted in one Stack Exchange question. But even "Why... a mirror but not a camera?" should contain a little bit of research or explanation. It was an array of retroreflectors and was totally passive; you set it down, align the bubble level and Sun-compass and it just sits there and reflects laser pulses for the next fifty years until eventually too much lunar dust settles on it. $\endgroup$
    – uhoh
    Jul 23 '21 at 0:23

Why did the astronauts leave a mirror but not a camera on the Moon?

The Apollo astronauts did leave a camera on the Moon. They left several cameras on the Moon. Most of those cameras were absolutely worthless after being left behind. Every kilogram of camera taken back to Earth represented a kilogram of Moon rocks that could not be taken back to Earth.

It's important to remember how low tech things were in the late 1960s / early 1970s. All of the high resolution imagery was captured on film. The astronauts took the film back to Earth but left behind the very expensive Hasselblad cameras used to take those pictures. Even though those cameras were extremely expensive, Moon rocks were even more valuable.

There were some ridiculously low grade cameras (low grade by current standards) on the Apollo missions that used broadcast technology rather than film. The most successful was the video camera left behind by the Apollo 17 mission. It captured the liftoff of the ascent module and then it lasted another another 27 hours before being overcome by high temperatures at lunar noon. The resolution was 320 lines by 200 pixels. In contrast, a modern cellphone has a resolution of 4032 x 3024 pixels.

Regarding the mirrors, the astronauts did not leave mirrors behind. They left behind something much more valuable to science. What they behind on the surface of the Moon were retroreflectors. There's a huge difference between mirrors and retroreflectors. When you shine a light on a mirror at an oblique angle, the light will reflect off of the mirror at the same oblique angle -- in the other way. You won't see the reflection. When you shine a light on a retroreflector at an oblique angle, the light will be reflected back to you.

Cameras are active devices. Cameras need power to point the camera, to capture imagery, and to transmit the captured imagery back to Earth. The low resolution video camera on Apollo 17 lasted for 27 hours after the ascent module left the surface of the Moon.

In contrast, retroreflectors are completely passive devices. The Apollo astronauts simply needed to place the retroreflectors on the surface of the Moon, with no power supply needed. Those lunar retroreflectors are still functioning to this day, albeit at a highly degraded capacity. The combination of high temperature ranges, solar radiation unfiltered by an atmosphere, and lunar dust have taken a high toll on those retroreflectors. But they are still working.


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