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Love this one!Wow! Lots of fantastic images here!
Here's my contribution. As is the case with nearly all astrophotography images, this single image is actually the result of combing many exposures.
Andromeda Galaxy & Companions by Tim Campbell, on Flickr
This is the Andromeda galaxy (aka Messier 31 or just "M31" for short). It's located in the constellation of Andromeda (hence the name) about 2.5 million light years away (so we see it as it used to look 2.5 million years ago). A light year is measure of distance, not time... it's the distance that light can travel (at about 186,000 miles/sec) in one year and works out to just shy of 6 trillion miles. So in rough round numbers... this galaxy is 2.5 million x 6 trillion miles away. The galaxy is much larger than our own (more than twice as wide) at 220,000 light years across. It contains about 1 trillion suns (a little over 3x more than our own Milky Way galaxy.)
We think of objects like our full moon as being very large objects in the night time sky... but even with the incredible distance to this galaxy... it is STILL more than 6 times wider than the full moon. (The full moon is about 1/2º from edge to edge... this galaxy is 3.1º from edge to edge.) We usually do not even notice it due to light pollution but it is visible to the unaided eye if you are observing on a moonless night from a dark sky location.
The image above required more than 1 hour of exposure time (8 exposures, each of which were 8 minutes long - using a telescope mount that is able to precisely track the movement of the sky.)