M8, also known as the Lagoon Nebula, is a giant spectacular emission nebula in Sagittarius that's one of the brightest and finest star forming regions in the entire sky. With an apparent magnitude of +6.0, it's faintly visible to the naked eye and a wonderful sight through all types of optical instrument.
The nebula was discovered by Italian astronomer Giovanni Hodierna sometime before 1654. French astronomer Guillaume Le Gentil independently found it in 1747 before Charles Messier added the object to his catalogue on May 23, 1764. The distance to M8 is uncertain. It's currently estimated at 5,200 light-years although it might be as close as 4,100 light-years or as far away as 6,000 light-years.
When seen from our perspective this is an extremely large object. It covers 90 by 40 arc minutes of apparent sky, which is many times larger than the full Moon and comparable in size to another celebrated star forming region, the Great Orion Nebula (M42). To locate M8, start by finding the bright teapot asterism of Sagittarius. The top three stars of the teapot are Kaus Borealis (λ Sgr - mag. +2.8), Kaus Media (δ Sgr - mag. +2.7) and φ Sgr (mag. +3.2). Now imagine a line connecting φ Sgr to Kaus Borealis and then extend it in a westerly direction, curving slightly southwards, for about 6 degrees until arriving at M8. The Trifid Nebula (M20) is located 1.5 degrees north of M8.
The Lagoon Nebula is best seen from southern and equatorial regions during the months of June, July and August.
When viewed through popular 7x50 or 10x50 binoculars, M8 appears as a oblong shaped cloud like patch of diffuse light that's slight brighter towards the centre. A scattering of faint stars are superimposed on the nebula. Small scopes of the order of 80mm (3.1-inch) aperture show the nebulosity split into two distinct sections, separated by a dark dust band. Through a larger 200mm (8-inch) telescope, M8 is a wonderful sight. The cloud is better defined with a noticeable brighter core. There are many twists, knots with numerous dark bands running through the centre. A large number of predominantly white stars can also be seen. Positioned at the eastern edge of M8 is NGC 6530, an open cluster of bright stars. Like many nebulae, when photographed or imaged M8 appears pink in colour, but to the eye through binoculars or telescopes it's either grey or has a green tint. This is a consequence of the poor colour sensitivity of the retina at low light levels.
Within the brightest part of the Lagoon Nebula is a feature known as the Hourglass Nebula. It was discovered by John Herschel and occurs in a region where intensive star formation appears to be taking place. M8 also contains a number of Bok globules, which are dark, collapsing clouds of dense dust and gas where star formation can take place. They are known to be some of the coldest objects in the universe and are still a subject of intense research. America astronomer E. E. Barnard catalogued many of these objects at the end of the 19th century.
M8 Data Table
|Object Type||Emission Nebula|
|RA (J2000)||18h 03m 41s|
|DEC (J2000)||-24d 22m 49s|
|Apparent Size (arc mins)||90 x 40|
|Radius (light-years)||70 x 30|
|Other Name||Sharpless 25|
|Notable Feature||Structure at centre is known as the Hourglass Nebula (not to be confused with better known Hourglass Nebula in Musca)|