Spiral Arms
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
APODs including "Spiral Arms"
Grand Design Spiral Galaxy NGC 2997
30/10/1996
NGC 2997 is a grand design spiral galaxy. Its small nucleus and sprawling spiral arms give it a type "Sc" designation. NGC 2997 is speeding away from us at about 1100 kilometers per second, which would place it at about 55 million light years distant, given current estimates of the expansion rate of our universe. NGC 2997 is thought to have a mass of about 100 billion times that of our Sun, but is probably less massive than our own Milky Way Galaxy. NGC 2997 is not seen face-on - it is thought tilted by about 45 degrees. NGC 2997 is particularly notable for a nucleus surrounded by a chain of hot giant clouds of ionized hydrogen.