Astronomy Picture of the Day - Nebulas and Clusters in Sagittarius

Explanation: Can you spot famous celestial objects in this image? 18th-century astronomer Charles Messier cataloged only two of them: the bright Lagoon Nebula (M8) at the bottom, and the colorful Trifid Nebula (M20) at the upper right. The one on the left that resembles a cat's paw is NGC 6559, and it is much fainter than the other two. Even harder to spot are the thin blue filaments on the left, from supernova remnant (SNR G007.5-01.7). Their glow comes from small amounts of glowing oxygen atoms that are so faint that it took over 17 hours of exposure with just...