All four objects on this awesome image are located in Sagittarius:
– The Lagoon Nebula (catalogued as Messier 8 or M8, and as NGC 6523) is a giant interstellar cloud. It is classified as an emission nebula and as a H II region. The Lagoon Nebula was discovered by Giovanni Hodierna before 1654 and is one of only two star-forming nebulae faintly visible to the naked eye from mid-northern latitudes. Seen with binoculars, it appears as a distinct oval cloudlike patch with a definite core. A fragile star cluster appears superimposed on it.
– The Trifid Nebula (catalogued as Messier 20 or M20 and as NGC 6514) is an H II region. It was discovered by Charles Messier on June 5, 1764. Its name means ‘divided into three lobes’. The object is an unusual combination of an open cluster of stars; an emission nebula (the lower, red portion), a reflection nebula (the upper, blue portion) and a dark nebula (the apparent ‘gaps’ within the emission nebula that cause the trifurcated appearance; these are also designated Barnard 85). Viewed through a small telescope, the Trifid Nebula is a bright and peculiar object, and is thus a perennial favorite of amateur astronomers.
– Messier 21 or M21 (also designated NGC 6531) is an open cluster of stars. It was discovered and catalogued by Charles Messier on June 5, 1764. M21 is a relatively young cluster of a mere 4.6 million years of age. It is tightly packed but contains about 57 stars. A few blue giant stars have been identified in the cluster, but Messier 21 is composed mainly of small dim stars. With a magnitude of 6.5, M21 is not visible to the naked eye; however, with the smallest binoculars it can be easily spotted on a dark night.
– NGC 6559 is a star forming region located at a distance of about 5000 light-years from Earth, showing both emission (red) and reflection (bluish) regions.
Baader Planetarium Ha 7nm : 18×900″ bin 1×1
Baader Planetarium OIII 8.5nm 2″: 13×900″ bin 2×2
Baader Planetarium SII 8nm: 9×900″ bin 2×2