Regions of stars and interstellar matter that extend from the center of spiral galaxies, forming a spiral pattern; in the Milky Way, these include the Orion Arm where our Solar System resides.
Source: esa.int
12/09/1995

Long winding spiral arms are clearly evident on this spectacular picture of the spiral galaxy M83. The blue color of the spiral arms is caused by the relatively large fraction of young blue stars there. Dark dust lanes are mixed in with the stars and trace the spiral structure of the galaxy. This galaxy contains many billions of stars, and its light took many millions of years to reach us. Our own Milky Way Galaxy would appear similar to this if viewed from M83! This picture is number eight on a publicly posted list of images from the Anglo-Australian Telescope (AAT).