M20 is the famous Trifid Nebula, a bright colourful emission and reflection nebula that's located in the constellation of Sagittarius. At magnitude +6.3, it's visible with binoculars. This remarkable object not only contains an emission and reflection nebula but also a dark nebula and an embedded open cluster. When photographed or imaged it looks spectacular, with the emission nebula appearing red, the reflection nebula blue and numerous dark lanes mixed in between. The dark lanes appear to cut through the nebula splitting it into three prominent sections, hence the popular name Trifid, which means divided into three lobes.
Charles Messier discovered both M20 and M21 on June 5, 1764. He referred to M20 as an envelope of nebulosity. The surrounding area of sky is the richest part of the Milky Way. Here you are looking towards the direction of the galactic centre, hence the abundance of stars, open clusters, globular clusters and nebulae. This wonderful region of sky is perfect to scan with binoculars or small telescopes, especially at low magnifications.
To locate the Trifid, first focus on the bright familiar teapot asterism of Sagittarius. The top three stars of the teapot are Kaus Borealis (λ Sgr - mag. +2.8), Kaus Media (δ Sgr - mag. +2.7) and φ Sgr (mag. +3.2). Imagine a line connecting φ Sgr to Kaus Borealis and then extending it for just over 6 degrees to arrive at M20.
The Trifid is best seen from southern and equatorial regions during the months of June, July and August.
M20 is a fine sight in 7x50 or 10x50 binoculars, appearing as fuzzy circular diffuse shape. A small 80mm (3.1-inch) telescope hints at dark lanes spreading from the center of the nebula, especially when viewed under dark skies. With a 150mm (6-inch) or 200mm (8-inch) scope, the Trifid becomes an exciting object. Its irregular shape is visible, along with the trisecting dark lanes, exquisite twists/turns and under good conditions hints of colour. Of course to really appreciate the full beauty of this object an image or photograph is required.
M20 is located 5,200 light-years from Earth and has a spatial diameter of 42 light-years. The dark nebula that gives the Trifid its appearance was cataloged by E. E. Barnard as Barnard 85 (B85) and in 2005 the Spitzer Space Telescope discovered 30 embryonic stars and 120 newborn stars, which had not been seen in visible light images.
M20 Data Table
|Object Type||Emission and Reflection Nebula|
|RA (J2000)||18h 02m 21s|
|DEC (J2000)||-23d 01m 38s|
|Apparent Size (arc mins)||28 x 28|
|Other Name||Collinder 360|