AstronomyPicture of the Day—20181219

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.

2018 December 19

M31:The Andromeda Galaxy

ImageCredit & Copyright: Robert Gendler

Explanation:What is the nearest major galaxy to our own Milky Way Galaxy? Andromeda. Infact, our Galaxy is thought to look much like Andromeda. Together these two galaxies dominate the Local Group of galaxies. The diffuse light from Andromedais caused by the hundreds of billions of stars that compose it. The several distinct stars that surround Andromeda's image are actually stars in our Galaxy that are well in front of the background object. Andromeda is frequently referred to as M31 since it is the 31st object on Messier's list of diffuse sky objects. M31 is so distant it takes about two million years for light to reachus from there. Although visible without aid, the featured image of M31 is adigital mosaic of 20 frames taken with a small telescope. Much about M31 remains unknown, including exactly how long it will be before it collides with our home galaxy.