Messier 17 is an emission nebula and star forming region lying about 5,500 light-years from Earth in the constellation Sagittarius. It may have more nicknames than any other nebula. It is known as the Swan Nebula because the bright central portion looks like a swan swimming on water with neck and head arching around the dark nebula near the center, with wings and tail behind, and a water line below. The neck and body of the swan look like a check mark, particularly through telescopes, so it is also known as the Check Mark Nebula. The bright portion wrapped around the dark nebula resembles a capital greek letter Omega, giving it the name the Omega Nebula. Similarly, a capital Omega looks like a horseshoe, which lends the name the Horseshoe Nebula.
Image Details:
Telescope/Mount: Celestron Compustar C14 with Starizona LF reducer/corrector (f/7.5).
Camera: SBIG STL 1100M with Baader Planetarium L,R,G,B filters.
Adaptive Optics: SBIG AO-L at 8 Hz.
Location: Pommier Observatory, Portland, OR, USA.
Dates: 2018-07-10 through 2018-07-18.
Exposures: Ha:R:G:B=450:40:30:30 = 9 hours, 10 minutes total exposure.