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M20 - Trifid Nebula in Sagittarius |
| 6/29/08,
12:30 AM Coyle Field, NJ Meade LX90 8" SCT, FL 1260 mm Meade DSI Pro II Camera 7 subs x 15 secs, unguided
Processed PS |
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Discovered by Charles
Messier in 1764.
The Trifid Nebula Messier 20 (M20, NGC 6514) in Sagittarius is a
remarkable and beautiful object as it consists of both a conspicuous
emission nebula and a remarkable reflection nebula component.
Charles Messier discovered this object on June 5, 1764, and described it
as a cluster of stars of 8th to 9th magnitude, enveloped in nebulosity,
where the remark on nebulosity follows only after the description of
nearby M21, and includes that object.
The Trifid Nebula M20 is famous for its three-lobed appearance. This may
have caused William Herschel, who normally carefully avoided to number
Messier's objects in his catalog, to assign four different numbers to
parts of this nebula: H IV.41 (cataloged May 26, 1786) and H V.10, H V.11,
H V.12 (dated July 12, 1784). That he numbered this object at all may have
its reason in the fact that Messier merely described it as 'Cluster of
Stars.' The name 'Trifid' was first used by John Herschel to describe this
nebula; this astronomer assigned only one catalog entry to the whole
object (h 1991, h 3718, GC 4355) which became J.L.E. Dreyer's NGC 6514.
The dark nebula, which is the reason for the Trifid's appearance, was
cataloged by Barnard as Barnard 85 (B 85).
The red emission nebula with its young star cluster near its center is
surrounded by a blue reflection nebula which is particularly conspicuous
to the northern end. The nebula's distance is rather uncertain, with
values between 2,200 light years (Mallas/Kreimer; Glyn Jones has 2,300)
and about 7,600 light years (C.R. O'Dell 1963). The Sky Catalog 2000 gives
5,200 light years, a value which is also used by Archinal and Hynes
(2003), and which we adopt here. The WEBDA database has 3140, the Hubble
Press Release of Jeff Hester (STScI-PRC99-42) gives "about 9000" light
years.
In the sky, the Trifid nebula M20 is situated roughly 2 degrees northwest
of the larger Lagoon Nebula M8, so that both nebulae form a nice target
for wide field photographs, as these images of the M8 and M20 region, or
the big DSSM image of this region. It is even closer to the open cluster
M21 and shows up in the upper left edge of our M21 image
*Much of the information regarding the Messier Objects and their origins has
been graciously provided by
www.seds.org/messier/
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Solar System
