Astronomy Picture of the Day Discover the cosmos! Each day a different image or photograph of our fascinating universe is featured, along with a brief explanation written by a professional astronomer. 2013 September 5 M1: The Incredible Expanding Crab Image Credit & Copyright: Adam Block, Mt. Lemmon SkyCenter, U. Arizona Explanation: The Crab Nebula is cataloged as M1, the first on Charles Messi..