This picture is of a spiral galaxy. A spiral galaxy consists of stars, dust, dark matter, and is held up by gravity. Spiral galaxies, like this one, have a flat disk, a bulging center, and surrounding spiral arms. Galaxies achieve their shape due to the environment around them. This happens from neighbor's influences and other galaxy collisions. The speed at which the galaxy rotates determines how pinwheel shape it appears.
This particular spiral galaxy, NGC 6946 = Caldwell 12, has the colors blue, red (purpleish), and yellow in it. Yellow stars tend to be in the middle of the galaxy. They are yellow stars because they are cooler and they are older. In the spiral arms one can find blue stars which are hotter, but short lived. The purple color regions represent hydrogen gas (red) and the blue stars. Those young blue stars are forming from the collapsing gas clouds.
The extent of the galaxy in the picture is 8.9 arcminutes. For an estimated distance of 22.5 Mly, this corresponds to a linear size of 58,000 ly.
Astrophysics. (2012, October 18). Retrieved December 14, 2012, from NASA: http://science.nasa.gov/astrophysics/focus-areas/what-are-galaxies/
Galaxies. (n.d.). Retrieved December 14, 2012, from National Geographic: http://science.nationalgeographic.com/science/space/universe/galaxies-article/
|Right Ascension (J2000)||20:34:52|
|Filters used||B (Blue), R (Red), V (Green), C (Clear)|
|Exposure time per filter||5 exposures of 60 seconds|
|Date observed||October 26, 2012 UT|