Comment by Arjuna | Hacker News Reader

Comment by Arjuna | Hacker News Reader

Some other interesting artifacts left on the Moon:

Lunar Laser Ranging Experiment arrays [1][2]. These are retro-reflectors that were left during the Apollo program. They are used for laser ranging. This is always good for getting a "deer in the headlights" look from conspiracy theorists when I explain that humans have been studying the distance between the Earth and the Moon with the arrays since 1969 to further our understanding of gravity, along with the knowledge of the Moon's increasing movement away from the Earth. Also, the Soviets deployed retro-reflectors on Lunokhod 1 in 1970 [3] and Lunokhod 2 in 1973 [4].

Fallen Astronaut [5] commemorates astronauts and cosmonauts that died while working on their respective space programs.

[1] https://en.wikipedia.org/wiki/Lunar_Laser_Ranging_experiment

[2] http://www.physics.ucsd.edu/~tmurphy/apollo/doc/Bender.pdf

[3] https://en.wikipedia.org/wiki/Lunokhod_1

[4] https://en.wikipedia.org/wiki/Lunokhod_2

[5] https://en.wikipedia.org/wiki/Fallen_Astronaut

> Lunar Laser Ranging Experiment arrays

I've always wondered why we don't have any actual photos of them (or anything else) sitting on the moon.

My understanding is that all earth-based telescopes don't have the resolution, and hubble can't focus down that close.

Hubble does not have the angular resolution to resolve the objects left behind on the moon; you can do the calculations for yourself.[1]

[1] http://en.wikipedia.org/wiki/Hubble_Space_Telescope

> I've always wondered why we don't have any actual photos of them (or anything else) sitting on the moon.

We do.

http://www.nasa.gov/sites/default/files/images/584392main_M1...

That picture is from Lunar Reconnaissance Orbiter Camera (LROC); you can find pictures of all the Apollo landing sites on its webpage.[1]

[1] http://featured-sites.lroc.asu.edu/

The moon is effectively at infinity in terms of focus. The problem is not that it can't focus, but just that the stuff is too small. Hubble has taken pictures of the moon.

The problem isn't focus, it's tracking rate. Hubble can take pictures of the moon, but not long exposures; it can't spin fast enough to follow the moon through its field of view, so it has to point where the Moon is going to be, then take the picture at the moment it passes through. https://what-if.xkcd.com/32/

http://xkcd.org/1441/

I hadn't thought of this when I first saw the comic: the moon is 1.3 light seconds away, so that is some improbably fast dialog (or some improbably slow light-based weapon).

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