1. The history
2. To find M20
3. To observe M20
4. The stars of M20 and more

The "Trifid Nebula", probably, was first observed by Le Gentil in 1747, during his observations of M8, and was rediscovered by Messier on Jun., 5, 1764. According to Burnham, Messier doesn't see the nebula, but only a cluster of faint stars, and describes the object as: "Cluster of stars a little above the Ecliptic between the bow of Sagittarius and the right foot of Ophiuchus...". In effect, Messier refers to same nebulosity in M20 in the description of M21, discovered in the same night ("... the stars of both clusters are 8-9 mag. and enveloped in nebulosity.")

Herschel first recorded the typical "trilobate" pattern of the southern portion of the nebula. John Herschel, probably, called it "Trifid Nebula".

M20 lies soma 1.5° NW from M8, the "Lagoon Nebula", and in the wide field photograph the two nebulae are a striking pair. With the addition of M21 a little NE of M20.

The red emission nebula, with the young star cluster close to his center, is surrounded from a blue reflection nebula, particularly conspicuous in the northern edges.

La distanza della nebulosa è abbastanza incerta: le valutazioni proposte vanno dai 2.200 a.l. ai 7.600.

The peculiar "trifid" pattern of the southern portion of the nebula spread out from the multiple star HN40 (or GC24537), a giant O7-type, with an absolute mag. of about -5.2; this star appears double in small telescopes, and as a multiple system in the bigger ones; the principal components are respectively of mag. 6.9, 8.0, and about 10.5. With the Lick Observatory's 36 inch telescope, S. W. Burnham found 6 stars in this system. The main star of the group seems to be the most important source of brightness for the nebula. But, probably, in the core of M20 there are several other very hot stars, hidden among the obscure matter of the nebula.