I’ve got a feeling that the neighbours cat is crapping in my yard and I want to catch it in the act in the most ostentatious way possible. Say I got control of the Hubble Space Telescope, currently in low Earth orbit and spotting distant galaxies. Could I turn it (or any other space-based telescope) towards Earth? Would the image I got prove the cat did the dirty deed or would the images be worthless to anyone?
I’m sure the details are more complex, but basically yes. American KH spy satellites are very similar to the HST in general design…
It’d be worthless, according to former Doper BadAstronomer. It’d be, at best, a cat-coloured blurred streak, if that.
Very different orbits, though.
The atmosphere pretty much limits effective pixel size to be at least 10cm.
Having more pixels (reducing them to 5cm or 2 cm or 1cm) isn’t giving any better detail, its just blur.
So no satellite is going to identify the cat, all it will show a cat as a few pixels… a 15 pixel cat isn’t high enough res… Spy satellites can prove a school bus drove across your back yard… not a cat
XKCD had a “what if” answering this exact question. Hubble
The Earth is also much brighter than the things the Hubble was designed to look at. If you’re not very careful about limiting your exposure times, you could burn out some of the instruments. It looked at the Moon once, but even that was pushing it, and the Earth is considerably brighter than the Moon.
Fascinating, thanks for the very thorough answers. Would I have better luck with its future successor, the James Webb Space Telescope? It seems planned to have a far larger orbit than Hubble.
You’d get less motion blur, but the brightness would be even more overwhelming, and the resolution would be far less, both due to the instrument and its distance.
Hubble is designed for optical wavelengths while the JWST is focused on infra-red.
Also, I think that focus could be a potential problem… Question: what is the resolution of the sensor on Hubble?
Focus won’t matter. The Hubble has a focal length of a few meters, and is orbiting at a height of hundreds of kilometers. That’s close enough to “infinity” for practical matters.
Why? Because of the clouds? The oceans? Or is moon rock just dark?
All of the above.