Pinwheel Galaxy

Facing us head-on, its spiral arms fan out in every direction — a galaxy that looks exactly like a pinwheel. In photographs, red star-forming regions are studded like jewels along the several blue spiral arms reaching out from its bright center. Its disk is tilted slightly to one side, showing the mark of being jostled by another galaxy that passed close by.

The Pinwheel Galaxy (M101) is a face-on spiral galaxy about 21 million light-years away in the direction of Ursa Major, and at roughly 170,000 light-years across it is far larger than the Milky Way. Star birth is vigorous, so numerous giant emission nebulae glow red along its spiral arms, and its lopsided, asymmetrically swollen disk is thought to be the result of a past gravitational encounter with a neighboring galaxy. Located near the end star of the Big Dipper's handle, it is a relatively easy galaxy to find.