CCD image taken with an ST-9E CCD camera thru our 20-inch F/8.1 telescope working at F/5.2. The field of view is about 13x13 arc minutes. This image only shows a portion of the nebula.
M-20 is a bright nebula in Sagittarius that is a typical emission nebula, being a large mass of glowing gas excited to emit radiation by a hot stars within it. It is known as the "Trifid Nebula" and is possibly a part of the same vast complex of nebulosity that includes the nearby Lagoon Nebula. LeGentil probably first observed it in 1747, during his examination of the Lagoon. M-20 was rediscovered by Messier in June 1764 but he seems to have seen it only as a cluster of faint stars. .
C. Messier: (June 5th, 1764) 'A Cluster of stars a little above the Ecliptic between the bow of Sagittarius and the right foot of Ophiuchus. Reviewed 22 Mar. 1781.'
Quote from Burnham's Celestial Handbook:
'Sir William Herschel found the nebulosity conspicuously divided by a curious pattern of dark lanes, and catalogued the brightest portions as four separate objects. John Herschel was probably the first to call it the "Trifid" Nebula, and described it as "consisting of 3 bright and irregularly formed nebulous masses, graduating away insensibly externally, but coming up to a great intensity of light at their interior edges where they enclose and surround a sort of 3-forked rift or vacant area, abruptly and uncouthly crooked and quite void of nebulous light... A beautiful triple star is situated precisely on the edge of one of these nebulous masses just where the interior vacancy forks into two channels".'
Click here for Hubble Space Telescope Image, and here for an American Astronomical Society press release on star formation in the nebula.
Click here for KAS Member Tony Pilato's photo of M-20.