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 constellation Sagittarius. 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. Seen with binoculars, it appears as a distinct oval cloudlike patch with a definite core. Within the nebula is the open cluster NGC 6530.
|H II region|
M8, the Lagoon Nebula
|Observation data: J2000 epoch|
|Right ascension||18h 03m 37s|
|Declination||−24° 23′ 12″|
|Distance||4,100 ly (1,250 pc)|
|Apparent magnitude (V)||6.0|
|Apparent dimensions (V)||90 × 40 arcmins|
|Radius||55 × 20 ly|
|Designations||Sharpless 25, RCW 146, Gum 72|
NGC 6523, NGC 6530,
The Lagoon Nebula is estimated to be between 4,000-6,000 light-years 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.
7 Sagittarii is a massive star in the southern zodiac constellation of Sagittarius which is located in the Lagoon Nebula (NGC 6530), although multiple sources have considered it a foreground star. It is a dim star but visible to the naked eye with an apparent visual magnitude of 5.37. The distance to this star can be determined from the annual parallax shift of 3.02±0.28 mas, yielding a value of roughly 1,100 light years. It is moving closer to the Sun with a heliocentric radial velocity of −11 km/s.Gray and Garrison (1989) listed a stellar classification of F2 II/III for this star, suggesting it is a K-type star with a spectrum showing mixed traits of a giant/bright giant. Houk and Smith-Moore (1978) had a similar classification of F2/3 II/III. This may indicate it is not a member of NGC 6530, since it shouldn't have evolved to this class from the O-type stars that still populate this cluster, and hasn't had time to evolve from a less massive cluster star.It is a suspected chemically peculiar star. The spectral class from the calcium K line has been given as A8 while the class determined from other metallic lines was F4, making it an Am star. This peculiarity is now considered doubtful.7 Sagittarii has an estimated 18 times the Sun's radius and is radiating 658 times the Sun's luminosity from its photosphere at an effective temperature of around 6,800 K.9 Sagittarii
9 Sagittarii (9 Sgr) is a massive binary star in the constellation Sagittarius. It has an apparent magnitude of 5.97.Emission nebula
An emission nebula is a nebula formed of ionized gases that emit light of various wavelengths. The most common source of ionization is high-energy photons emitted from a nearby hot star. Among the several different types of emission nebulae are H II regions, in which star formation is taking place and young, massive stars are the source of the ionizing photons; and planetary nebulae, in which a dying star has thrown off its outer layers, with the exposed hot core then ionizing them.Engraved Hourglass Nebula
The Engraved Hourglass Nebula (also known as MyCn 18) is a young planetary nebula in the southern constellation Musca. It was discovered by Annie Jump Cannon and Margaret W. Mayall during their work on an extended Henry Draper Catalogue (the catalogue was built between 1918 and 1924). At the time, it was designated simply as a small faint planetary nebula. Much improved telescopes and imaging techniques allowed the hourglass shape of the nebula to be discovered by Raghvendra Sahai and John Trauger of the Jet Propulsion Laboratory on January 18, 1996. It is conjectured that MyCn 18's hourglass shape is produced by the expansion of a fast stellar wind within a slowly expanding cloud which is denser near its equator than its poles. The vivid colours given off by the nebula are the result of different 'shells' of elements being expelled from the dying star, in this case helium, nitrogen, oxygen and carbon.
The Hourglass Nebula was photographed by the Wide Field and Planetary Camera 2 of the Hubble Space Telescope.
A less-famous "Hourglass Nebula" is located inside the Lagoon Nebula.Gum catalog
The Gum catalog is an astronomical catalog of 84 emission nebulae in the southern sky. It was made by the Australian astronomer Colin Stanley Gum (1924-1960) at Mount Stromlo Observatory using wide field photography. Gum published his findings in 1955 in a study entitled A study of diffuse southern H-alpha nebulae which presented a catalog of 84 nebulae or nebular complexes. Similar catalogs include the Sharpless catalog and the RCW catalog, and many of the Gum objects are repeated in these other catalogs.
The Gum Nebula is named for Gum, who discovered it as Gum 12; it is an emission nebula that can be found in the southern constellations Vela and Puppis.HD 165516
HD 165516 is a blue supergiant star in the constellation Sagittarius. It is part of the Sagittarius OB1 association and appears against a rich Milky Way starfield near the Triffid Nebula and Lagoon Nebula.
HD 165516 is close to a small reflection and emission nebula, and an associated loose open cluster. The nebula is catalogued as GN 18.05.6, but was first listed as VdB 113. That name has since been used for the cluster itself, which is likely more distant than HD 165516. The whole cluster is less than a quarter of a degree across, with dozens of members from 8th magnitude downwards. V4381 Sagittarii is listed as a probable member, while HD 165516 and the nearby Wolf-Rayet star WR 111 are considered unlikely to be members.Home (Battlestar Galactica)
"Home" is a two-part episode of the reimagined Battlestar Galactica television series. Part 1 aired originally on the Sci Fi Channel on August 19, 2005, and Part 2 aired on August 26, 2005.
In the episode, Starbuck returns to the human fleet bearing the Arrow of Apollo. President Laura Roslin leads a team to the surface of Kobol to find the Tomb of Athena and a map to Earth. Commander William Adama overcomes his anger at Roslin and her allies and joins them on Kobol, where the Tomb provides a clue to Earth's location. The fleet is reunited.
According to executive producer David Eick, who wrote Part 1 and co-wrote Part 2 with executive producer Ronald D. Moore, "Home" is more about character development and relationships than about story. The episode received favorable critical review.Interstellar cloud
An interstellar cloud is generally an accumulation of gas, plasma, and dust in our and other galaxies. Put differently, an interstellar cloud is a denser-than-average region of the interstellar medium, (ISM), the matter and radiation that exists in the space between the star systems in a galaxy. Depending on the density, size, and temperature of a given cloud, its hydrogen can be neutral, making an H I region; ionized, or plasma making it an H II region; or molecular, which are referred to simply as molecular clouds, or sometimetimes dense clouds. Neutral and ionized clouds are sometimes also called diffuse clouds. An interstellar cloud is formed by the gas and dust particles from a red giant in its later life.Lagoon (disambiguation)
A lagoon is a body of water separated from the ocean by barrier islands, sand bars, or reefs.
Lagoon may also refer to:
A type of low-cost wastewater treatment system
Lagoon, a Super NES video game
Lagoon, an amusement park located in Farmington, Utah
A song on the album Century Child by Nightwish
Lagoon, an indie rock band
Lagoon, a 2014 novel by Nnedi Okorafor.See also:
EstuaryList of Hubble anniversary images
List of Hubble anniversary images is a list of images released to celebrate the Hubble Space Telescope anniversaries. They celebrate its "birthday" when it was launched into orbit on April 24, 1990 by the Space Shuttle with its crew.List of dark nebulae
This is a list of dark nebulae (absorption nebulae), also called "dark clouds".List of diffuse nebulae
Reflection nebulaNGC 6530
NGC 6530 is an open cluster in the constellation Sagittarius. It has a diameter of 10 arc minutes, with stars as bright as 7th magnitude. It exists within nebula Messier 8, the Lagoon Nebula.NGC 6544
NGC 6544 is a small globular cluster visible in the constellation Sagittarius. It is magnitude 7.5, diameter 1 arc minute. It is less than 1 degree southeast of Messier 8, the lagoon nebula.NGC 6553
NGC 6553 is a globular cluster in the constellation Sagittarius. NGC 6553 has an apparent magnitude of about 8 magnitudes with an apparent diameter of 8.2 arcminutes. Its Shapley–Sawyer Concentration Class is XI, meaning the star concentration is very loose even at the center; it has stars of magnitude 20 and dimmer. It is located just over a degree southeast of Messier 8, the Lagoon Nebula.Nebulae in fiction
Nebulae, often being visually interesting astronomical objects, are frequently used as settings or backdrops for works of science fiction.Sagittarius (constellation)
Sagittarius is one of the constellations of the zodiac. It is one of the 48 constellations listed by the 2nd-century astronomer Ptolemy and remains one of the 88 modern constellations. Its name is Latin for the archer, and its symbol is (Unicode U+2650 ♐), a stylized arrow. Sagittarius is commonly represented as a centaur pulling back a bow. It lies between Scorpius and Ophiuchus to the west and Capricornus and Microscopium to the east.
The center of the Milky Way lies in the westernmost part of Sagittarius (see Sagittarius A).Southern African Large Telescope
The Southern African Large Telescope (SALT) is a 10-metre class optical telescope designed mainly for spectroscopy. It consists of 91 hexagonal mirror segments each with a 1-metre inscribed diameter, resulting in a total hexagonal mirror of 11.1 m by 9.8 m. It is located close to the town of Sutherland in the semi-desert region of the Karoo, South Africa. It is a facility of the South African Astronomical Observatory, the national optical observatory of South Africa.
SALT is the largest optical telescope in the southern hemisphere. It enables imaging, spectroscopic, and polarimetric analysis of the radiation from astronomical objects out of reach of northern hemisphere telescopes. It is closely based on the Hobby-Eberly Telescope (HET) at McDonald Observatory, with some changes in its design, especially to the spherical aberration corrector. It shares the same fixed mirror altitude design, with access to 70% of the visible sky. The main driver for these changes were desired improvements to the telescope's field of view.
First light with the full mirror was declared on 1 September 2005, with 1 arc second resolution images of globular cluster 47 Tucanae, open cluster NGC 6152, spiral galaxy NGC 6744, and the Lagoon Nebula being obtained. The official opening by President Thabo Mbeki took place during the inauguration ceremony on 10 November 2005.South Africa contributed about a third of the total of US$36 million that will finance SALT for its first 10 years (US$20 million for the construction of the telescope, US$6 million for instruments, US$10 million for operations). The rest was contributed by the other partners - Germany, Poland, the United States, the United Kingdom and New Zealand.
See also: Gum Nebula