Stephan's Quintet: 300 Million Light Years
The telescopic view of this cluster of galaxies in Pegasus has been compared to a group of ghosts hanging there in the eyepiece. This is a fitting description of the experience -- when we observe these distant objects we're looking at images from 300 million years ago, when the first amphibians evolved on earth. This was the late Carboniferous, known for its swamps, where you might meet some very early reptiles, ancestors of the dinosaurs. Trilobites were getting scarce. Here's some maps of the world at that time; the continents we know today were still part of the Pangean landmass.