Galaxy NGC 6946 in Cepheus,  Caldwell 12
Why is the shape of some galaxies spiral?  Most astronomers believe that density waves are triggered by gravitational interactions between neighboring
galaxies.  These density waves compress interstellar matter into spiral arms, forming diffuse nebula that evolve into starforming regions and clusters of stars.  
Other astronomers feel that spiral structure requires the collision of two or more galaxies, which gives rise to rotation of spiral arms of billions of stars around a
central denser core.  Because this process requires hundreds of millions of years to occur, no one I know has witnessed this event. Astronomers rely on
computerized models to make predictions (educated guesses) about galactic evolution.

When viewed from "above" or "below," the spiral shape is most clearly seen.  When viewed from the side, as in the
Sombrero Galaxy and the Outer Limits  
Galaxy NGC891, the spiral shape is concealed.
The Galaxy NGC6946 glows at 9th magnitude in the constellation Cepheus.  Light from the galaxy traveled 15 million years to reach my camera.  Exposure was
190 minutes luminance unbinned, and 60 minutes each red, green, and blue exposures binned 2x2 with an ST10XME camera with a 0.67x reducer through a
Meade 12" LX200R.

My brother-in-law Douglas responded to this image with the following comments:

"Thanks for the picture of Galaxy NGC6946.  I have actually been there.  We just call it "46NG" for short.   One of the planets there has a great  Reguliun Worm
dish there.  You can't get it here.   I hate to say it but, your picture of 46NG does look a little dated.   You might want to think about getting a little closer next time.

All the best.   Douglas"
Music:  Star Wars theme