I recently saw a photo somebody posted of a galaxy 50 million light years away. I have always wondered, why doesn’t he point it at the moon or even a planet 10 light years away and see the surface up close? We might see water or certain organisms. I have yet to see a picture like that in my lifetime. Thanks in advance for the answer.
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Arcsecs of a Milky Way-sized galaxy 50 million lightyears away:
D = θ d / 206,265 –> θ = (D*206,265)/d)
Where D = size of galaxy, θ arcsecs, and d = distance to galaxy
100000 LY = (θ * 50000000 LY)/206265 => **θ = 412.53 arcsecs**
Arcsecs of coin-sized rock on the Moon:
0.00001 km = (θ * 384400 km)/206265 => **θ = 0.0000054 arcsecs**
So, the galaxy you’re talking about is about 70 million times larger than the small rock on the moon, from the PoV of Earth. To add to that, the galaxy is also much brighter.
Now, let’s look at what would be the smallest object the Hubble Telescope (with a resolution of 0.04 arcsecs) would be able to see on the Moon:
D = (0.04 * 384400 km)/206265 => **D = 74.5 m**
This means that a squareish or roundish object that is 75 m across would, if places perfectly, take up one pixel on a perfect Hubble Telescope image. And if that object was a rock on the moon, that pixel would be roughly the same color as all the pixels around it. This resolution can be increased a bit by taking multiple images with a very slight change in in the Hubble Telescope’s direction and then algorithmically stitching these images together.
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