M31 - Andromeda Galaxy
It lies about 2.5 million light-years from Earth. If our eyes could perceive it the way it appears in this photo, it would have an apparent size of 4-5 times the diameter of the Moon! And yet it is so distant, and its light so faint, that it vanishes from our sight. The object's diameter is roughly 152,000 light-years, give or take 25,000 light-years. This is Andromeda, M31, the spiral galaxy closest to our own.
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