A striking example of a spiral galaxy is M101, whose relatively close distance of about 27 million light years allows it to be studied in some detail. Recent evidence indicates that a close gravitational interaction with a neighboring galaxy created waves of high mass and condensed gas which continue to orbit the galaxy center. These waves compress existing gas and cause star formation. One result is that M101, also called the Pinwheel Galaxy, has several extremely bright star-forming regions (called HII regions) spread across its spiral arms. M101 is so large that its immense gravity distorts smaller nearby galaxies.

Date: May and June 2009
Location: St. Augustine, Florida
Optics: Ritchey-Chretien 10" f/7.35
Mount: AP 1200 GTO on Portable Pier
Camera: SBIG STl-6303E
Guiding: Astrodon OAG with Starlight Lodestar camera
Exposure: LRGB: Luminance: 12x15 minutes; RGB: 8x15 Minutes each
Processing: CCDStack and PhotoshopCS4