Messier 8

M8, also known as the Lagoon Nebula or NGC 6523, Sharpless 25, RCW 146, Gum 72, is a large, bright emission nebula located in the constellation Sagittarius. Classified as an H II region, the star-forming nebula has an apparent magnitude of 6.0 and lies at a distance of 4,100 light-years from Earth; right ascension 18h 03m 37s and declination -24°23’12”, with a radius of 110 x 50 light-years. The cluster is only about 2 million years old. The hot young stars in it are responsible for the nebula’s glow. The brightest star in the cluster belongs to the spectral class O5 and has an apparent magnitude of 6.9. Messier 8 never rises very high above the horizon for observers north of the equator, but can be seen in the summer months, when Sagittarius is prominent on the southern horizon when observed from northern latitudes. M8 is located just above and to the right of the Teapot asterism in Sagittarius. It can be found about 5 degrees west of Lambda Sagittarii, the star that marks the top of the Teapot. It is currently undergoing a period of active star formation and has already formed a sizable cluster of stars. The large, lagoon-shaped band of dust seen to the left of the cluster’s centre is what earned the Lagoon Nebula its name. The faint extension of the nebula to the east, spanning about 25 light-years, has its own designation in the Index Catalogue of Nebulae and Clusters of Stars: IC 4678. The nebula’s apparent size is about three times the size of the full Moon. The surrounding region contains a number of notable deep-sky objects, starting with the Trifid Nebula (Messier 20), which lies only half a degree north of the Lagoon. The open cluster Messier 21 and the globular cluster Messier 28 also lie in the vicinity. The globular cluster NGC 6544 is located a degree to the southeast of M8, and NGC 6553, yet another globular, lies another degree to the southeast.

To celebrate its 28th anniversary in space the NASA/ESA Hubble Space Telescope took this amazing and colourful image of the Lagoon Nebula. The whole nebula, about 4000 light-years away, is an incredible 55 light-years wide and 20 light-years tall. This image shows only a small part of this turbulent star-formation region, about four light-years across. This stunning nebula was first catalogued in 1654 by the Italian astronomer Giovanni Battista Hodierna, who sought to record nebulous objects in the night sky so they would not be mistaken for comets. Since Hodierna’s observations, the Lagoon Nebula has been photographed and analysed by many telescopes and astronomers all over the world. The observations were taken by Hubble’s Wide Field Camera 3 between 12 February and 18 February 2018.

M8 was discovered by the Italian astronomer Giovanni Battista Hodierna before 1654. Hodierna listed the nebula as No. II.6 in his catalogue. English astronomer John Flamsteed discovered the object independently around 1680 and added it as No. 2446 to his catalogue. In 1746, Swiss astronomer Jean-Philippe Loys de Chéseaux resolved some of the stars in M8 and classified it as a cluster. The following year, French astronomer Guillaume Le Gentil observed both the Lagoon Nebula and the associated cluster. Nicolas Louis de Lacaille listed the nebula in his 1751-52 catalogue as Lacaille III.13 and described it as “three stars enclosed in a drag of a nebula parallel to the Equator.” The category III in Lacaille’s catalogue was reserved for “nebulous stars.” Charles Messier added the object to his catalogue as Messier 8 on May 23, 1764. The German-British astronomer William Herschel catalogued two objects within M8 separately: H V.9 (GC 4363, NGC 6526) and H V.13 (GC 4368, NGC 6533). His son John Herschel listed the cluster NGC 6530 separately as h 3725 (GC 4366) and catalogued the Lagoon Nebula as h 3723 (NGC 6523, GC 4361).

This new infrared view of the star formation region Messier 8, often called the Lagoon Nebula, was captured by the VISTA telescope at ESO’s Paranal Observatory in Chile. This colour picture was created from images taken through J, H and Ks near-infrared filters, and which were acquired as part of a huge survey of the central parts of the Milky Way. The field of view is about 34 by 15 arc minutes. Image: ESO/VVV

Messier 8 is one of two star-forming nebulae that can be seen without binoculars from mid-northern latitudes. The other one is the Orion Nebula, or Messier 42 (NGC 1976), the famous diffuse nebula located in Orion constellation. The Nebula contains many Bok globules, or dark clouds of dense dust, in which new stars are being formed. These dark nebulae are collapsing proto-stellar clouds of material about 10,000 astronomical units in diameter. The most prominent Bok globules in the Lagoon Nebula were catalogued by the American astronomer Edward Emerson Barnard as Barnard 88 (B88), Barnard 89 (B89) and Barnard 296 (B296). B88 is comet-shaped and 0.5′ wide, and it extends from north to south for 2.7′ just above the star 9 Sagittarii. B296 is long and narrow and can be seen at the nebula’s south edge, while B89 is found in the region of the open cluster.

Like a Dali masterpiece, this image of Messier 8 from the NASA/ESA Hubble Space Telescope is both intensely colourful and distinctly surreal. Located in the constellation of Sagittarius (The Archer), this giant cloud of glowing interstellar gas is a stellar nursery that is also known as the Lagoon Nebula. Although the name definitely suits the beauty of this object, “lagoon” does suggest tranquillity and there is nothing placid about the high-energy radiation causing these intricate clouds to glow. The massive stars hiding within the heart of the nebula give off enormous amounts of ultraviolet radiation, ionising the gas and causing it to shine colourfully, as well as sculpting the surrounding nebula into strange shapes. A result is an object around four to five thousand light-years away which, on a clear night, is faintly visible to the naked eye. Since it was first recorded back in 1747 this object has been photographed and analysed at many different wavelengths. By using infrared detectors it is possible to delve into the centre of these dusty regions to study the objects within. However, while this optical image, taken with the Advanced Camera for Surveys (ACS) on the Hubble Space Telescope, cannot pierce the obscuring matter it is undoubtedly one of the most visually impressive. Messier 8 is an enormous structure — around 140 by 60 light-years in extent — to put this in perspective the orbit of Neptune stretches only about four light-hours from our own Sun. This image depicts a small region in the centre of the nebula, while the region adjacent to the Lagoon Nebula, from the same Hubble observations, can be seen here. This picture was created from exposures taken with the Wide Field Channel of the Advanced Camera for Surveys on Hubble. Light from glowing hydrogen (through the F658N filter) is coloured red. Light from ionised nitrogen (through the F660N filter) is coloured green and light through a yellow filter (F550M) is coloured blue. The exposure times through each filter are 1560 s, 1600 s and 400 s respectively. The blue-white flare at the lower left of the image is scattered light from a bright star just outside the field of view. The field of view is about 3.3 by 1.7 arc minutes. Image: ESA/Hubble & NASA

Messier 8 also contains a region known as the Hourglass Nebula, a bright knot of dust and gas, located in the nebula’s bright central region. The Hourglass Nebula was named by the English astronomer John Herschel, who discovered it. It should not be confused with the more famous Engraved Hourglass Nebula (MyCn 18), which lies in the constellation Musca, the Fly. The brightest region of M8 is a site of ongoing star formation. The Hourglass is illuminated by the extremely hot, young stars.  It lies near 9 Sagittarii, one of the brightest stars associated with Messier 8. 9 Sagittariii belongs to the spectral class O5 and has an apparent magnitude of 5.97. The Lagoon Nebula also contains funnel-like structures, created by an O-type star emitting ultraviolet light that heats up and ionizes the gases on the surface of M8. There are at least two such structures in the nebula’s central region, each spanning about half a light-year. The area is illuminated by Herschel 36, an extremely bright star with the stellar classification of O7 V and a visual magnitude of 9.5. The first direct proof of star-forming activity by accretion within M8 was discovered in 2006 when scientists found the first four Herbig-Haro objects within the Hourglass structure. Herbig-Haro objects are small patches of nebulosity that are formed when jets of gas ejected by newly formed stars from their poles collide with nearby dust and gas at high speeds. They are frequently found near very young stars. Credits: Messier Objects, Wikipedia.