The
Lagoon Nebula (catalogued as
Messier 8 or
M8,
NGC 6523,
Sharpless 25,
RCW 146, and
Gum 72) is a giant
interstellar cloud in the
constellationSagittarius. It is classified as an
emission nebula and as an
H II region.The Lagoon Nebula was discovered by
Giovanni Hodierna before 1654 and is one of only two star-forming
nebulae faintly visible to the eye from mid-northern latitudes. The Lagoon Nebula is estimated to be between 4,000-6,000
light-years away from the
Earth. In the sky of Earth, it spans 90' by 40', which translates to an actual dimension of 110 by 50 light years. Like many nebulas, it appears pink in time-exposure color photos but is gray to the eye peering through
binoculars or a
telescope, human
vision having poor color sensitivity at low light levels. The nebula contains a number of
Bok globules (dark, collapsing clouds of protostellar material), the most prominent of which have been catalogued by
E. E. Barnard as B88, B89 and B296. It also includes a funnel-like or
tornado-like structure caused by a hot
O-type star that emanates
ultraviolet light, heating and ionizing gases on the surface of the nebula. The Lagoon Nebula also contains at its centre a structure known as the Hourglass Nebula (so named by
John Herschel), which should not be confused with the better known
Engraved Hourglass Nebula in the constellation of
Musca. In 2006 the first four
Herbig–Haro objects were detected within the Hourglass, also including
HH 870. This provides the first direct evidence of active star formation by accretion within it.
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