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NGC 6523
Lagoon Nebula
, Messier 8, LBN 25
RA 18:04:15
Dec -24°19.3'
Bright
nebula |
Also known as the Lagoon Nebula, it is plainly
visible to the naked eye as a glowing patch just off the main stream of the
Sagittarius Milky Way. Burnham notes that the discovery of M8 is often credited
to Le Gentil in 1747, who described it as “a small nebulosity like the tail
of a comet with numerous stars... like the more transparent and whitish
localities of the Milky Way.” Burnham further writes that “it seems
that it was recorded by Flamsteed as a “nebulosum” preceding the “Bow
of Sagittarius” as early as 1680; de Cheseaux in 1746 also refers to a “cluster
in Sagittarius' bow.”
Lacaille included it in his 1755 catalogue as
Class III No. 13. In his half-an-inch 8x telescope he saw it as “three
stars in nebulosity parallel to the Equator.”
Messier observed it in 1764, describing at as “a
cluster which looks like a nebula in an ordinary telescope of three feet but in
a good instrument one observes only a large number of small stars... A fairly
bright star nearby is surrounded with a very faint glow; this is 9 Sagittarii, 7
mag. The cluster appears elongated NE-SW. Diam 30'.”
Sir William Herschel described it as “an
extensive milky nebulosity divided into two parts; the north part being the
strongest. Its extended exceeds 15'; the southern part is followed by a parcel
of stars.” In the Appendix to the 1912 'Scientific Papers of Sir William
Herschel' this object is described as “1784, May 22. Large, extended,
pretty bright, broad. The nebulosity of the milky kind, there are some pB stars
in it, but they seem to have no connection with it, being of very different
sizes and colours and resembling the other stars that are everywhere scattered
about in this neighbourhood. This is probably the star surrounded with
nebulosity mentioned by Messier. There is indeed one of the stars which are in
the nebula that is somewhat larger than the rest and may be the only one he saw.”
Sir John Herschel saw it as “a collection
of nebulous folds and matter surrounding and including a number of dark, oval
vacancies and in one place coming to so great a degree of brightness as to offer
the appearance of an elongated nucleus. Superimposed on this nebula and
extending in one direction beyond its area, is a fine and rich cluster of
scattered stars which seems to have no connection with it as the nebula does
not, as in the region of Orion, show any tendency to congregate about the
stars..” At the Cape of Good Hope, he observed it with an 18-inch f/13
speculum telescope. He recorded it as “A noble nebula; to be monographed.
The star taken is = 9 Sagittarii 7m. It is followed by a great cluster VI.13, of
which with the nebula fills many fields.” On a second occassion he called
it “a superb nebula... See plate 1, fig 1.”
Webb called it “a splendid galaxy object,
visible to naked eye. In a large field we find a bright coarse triple star,
followed by a resolvable luminous mass, including two stars, or starry centres,
and then by a loose and bright cluster enclosed by several stars; a very fine
combination...”
C E Barns wrote of it as “myriads of
low-mag stars and a few brighter units resembling somewhat the Pleiades,
involved in wide wastes of incandescent hydrogen and helium, overflung with dark
absorbing patches..”
Hartung notes that “this fine nebula
needs a large field and shows very extensive luminosity of varying brightness,
involving two bright stars, with irregular lanes and followed by a bright open
cluster... The whole field is wonderfully fine and varied, and small apertures
show it well.”
Burnham notes that the western half of M8 “is
dominated by two bright stars just 3' apart; the southern star is 9
Sagittarii... Just 3' WSW from 9 Sagittarii lies the brightest segment of the
nebulosity, a 'figure 8' shaped knot about 30” in size and often called
from its shape “The Hourglass”...”
David Neilson (Oakland, California, USA),
writes in the The Webb Society Nebulae and Clusters Section Report No. 10, July
1992: “Roughly bar-shaped, misty nebula surrounding four stars (mag 10-11).
Due east, the dark rift is very distinct and is followed by a large, indistinct
region of nebulosity (8-inch).”
John Bortle (Webb Society Quarterly Journal,
January 1976) using 10x50 binoculars, estimates the visual magnitude of NGC
6523+6530 as 3.7.
Beverly Lynds (Astrophysical Journal
Supplement, No 105, 1965) in her Catalogue of Bright Nebulae, notes that its
maximum size is 45' x 30'.
Tom Lorenzin: “5M; 80' x 40' extent!
easily found with naked eye or binoculars; dark lane winds thru SW to NE; in E
segment lies 1' diameter “HOURGLASS”, 3' WSW of 9 SGR, illumination
source; dark void surrounds 12M star just W of Hourglass's constriction; use
high-x; cluster N6530 (10' diameter; 25-plus 7M and dimmer members) in N part of
E segment; N-filter aids greatly; called “LAGOON”; one more of the
best!.”
Donald J. Ware:”The Lagoon Nebula. With
the possible exception of the Great Orion Nebula (M-42), this is probably the
finest cluster and nebula combination in the heavens. A large and loosely
scattered open cluster is seen in juxtaposition with a large and swirling mist
of nebulosity. Many dark regions can be seen in looping patterns which are
highlighted by the brighter regions. This object is easily seen in finder
scopes, binoculars, and with the naked eye.”
Steve Coe, observing with a 13” f/5.6,
notes: “(M 8) Very bright, very, very large, somewhat compressed cluster
with lots of nebulosity. With the 2" eyepiece that gives a one degree field
with the 13", the entire field is nebulous and the dark lane that gives the
Lagoon its' name is obvious. I counted 40 stars included within the cluster and
there are another 50 stars among the outer parts of the nebula and 10 of the
stars are within the dark lane. Going to 100X shows the west side of the
nebulosity is brightest and adding the UHC makes the nebula grow 1.5 times in
size. I don't like the view with the UHC filter because it dims the stars
involved and that is a large part of the beauty of this area of the sky. The
Lagoon is an obvious naked eye spot in the Milky Way, even on a mediocre
evening. In the finder or 10X50 binoculars this area in spectacular, the Lagoon
and Trifid fit in the same field with star chains and dark lanes winding their
way through the entire field of view. This part of Sagittarius will be a
favorite as long as people construct telescopes.” |
