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Object Name: Messier 8
Alternative Designations: M8, NGC 6523, Sharpless 25, RCW 146, Gum 72, Lagoon Nebula
Object Type: Emission Nebula
Right Ascension: 18 : 03.8 (h:m)
Declination: -24 : 23 (deg:m)
Distance: 5.2 (kly)
Visual Brightness: 6.0 (mag)
Apparent Dimension: 90×40 (arc min)
Locating Messier 8: Although the constellation of Sagittarius is recognized as the Archer, it is most familiar as an asterism known as the ‘teapot’. Where skies are dark, its simple house-like shape appears like a teapot in the sky and the steam escaping the spout in the Milky Way. Finding Messier 8 in binoculars or a telescope is easy in a dark location, because you only need to start at the tip of the teapot’s spout and move your optics due north until this large, bright nebula appears. However, not everyone is blessed with dark skies and finding M8 from an urban location can be a little more difficult. From a well-lighted situation, both the teapot lid star (Lambda) and Alpha Scorpii (Antares) show well. You’ll find M8 just slightly north about 1/4 of the distance between Lambda and Alpha. In binoculars it will be quite bright and you’ll see the beginnings of its embedded open cluster – while a telescope of any size will resolve the cluster and bring up wonderful details in the wispy nebula. Large aperture should also look for accompanying dark nebula, too. Be aware that although it is bright, well-lit situations will greatly reduce contrast and a moonlit night or city lights will make it very difficult to find. Because of the Lagoon Nebula’s large apparent size, use low magnification to see the full extent of the nebula, but be sure to up the power to study its many features!
What You Are Looking At: Messier Object 8 is a giant interstellar cloud. An emission nebula is a localized region of ionized gas which emits light in different colors at wavelengths not always visible to the human eye. Its energy source is ionization from high-energy photons emitted from a nearby hot star, which causes it to glow – much like the heating coil on an electric stove. The colors you see photographically depend on the chemical composition and how much it is being ionized. Most nebulae contain an abundance of hydrogen, which doesn’t require much energy to be ionized and appears red. Where more energy is available from more powerful stars, other elements will be ionized and green and blue hues will appear. To our human eyes, we see nebulae like M8 is gray, or gray/green… Doubly ionized oxygen! Many emission nebulae like M8 often have dark areas in them where no stars or light seems to appear. We refer to these as ‘dark nebula’ but they’re really just clouds of dust which block the light.
The Lagoon Nebula is about 5200 light years away and covers an area of space about 140 by 60 light years. Its brightest portion is often called the “Hourglass Nebula” and it’s a region where new star formation is occurring. Inside you’ll also see young open star cluster NGC 6530. According to information, it may be situated just slightly in front of the nebula from our perspective, but interstellar reddening shows the nebula is also involved with the cluster. M8 is also famous for its Bok globules – dark, collapsing clouds of protostellar material. They were first discovered by E. E. Barnard and cataloged as B88, B89 and B296.
In this picture taken by the Hubble Space Telescope, is an area spanning about 5 light years. “At the center of the Lagoon Nebula is a whirlwind of spectacular star formation. Visible on the upper left, at least two long funnel-shaped clouds, each roughly half a light-year long, have been formed by extreme stellar winds and intense energetic starlight. The tremendously bright nearby star, Hershel 36, lights the area. Vast walls of dust hide and redden other hot young stars. As energy from these stars pours into the cool dust and gas, large temperature differences in adjoining regions can be created generating shearing winds which may cause the funnels.”
History: The Lagoon Nebula was discovered by Hodierna about 1654 and recovered by Guillaume Le Gentil in 1747 and independently noted as a “nebula” by John Flamsteed about 1680, who cataloged it as his Number 2446. Fortunately, in 1746 Philippe Loys de Cheseaux was also peering southward. Although he couldn’t see the nebula, he did classify it as a cluster. A year later Guillaume Le Gentil picked it up, and noted both: “The first [nebula] is between the left heel of Serpentarius [Ophiuchus] and the bow of Sagittarius, to the west of a star cluster which is located in this place in the sky, and which appears the same at eyesight, rather resembling the nebula of Cancer [Praesepe, M44]: That nebula has exactly the shape of an equilateral triangle, a bit elongated, and the turning point to the south-west. I have observed it with a refractor of 18 to 20 feet [FL], and it always appeared to me nebulous and transparent; it touches with its base a rather beautiful star, seen in the refractor, and which is the brightest of all those which compose the star cluster I have mentioned. The right ascension of this star is for the beginning of 1748, 266d 44′ 22″ [17h 46m 57s], its southern declination, 25d 8′ 10″, its [ecliptical] longitude, 26d 45′ 00″, and its southern [ecliptical] latitude 1d 30′ 00″.
Nicholas Louis de Lacaille had written down the Lagoon Nebula in his 1751-52 works as Lacaille III.14. But when Charles Messier cataloged this object on May 23, 1764, it became famous at last: “I also have determined, in the same night [May 23 to 24, 1764], the position of a small star cluster which one sees in the form of a nebula, if one views it with an ordinary [non-achromatic] refractor of 3 feet [FL], but when employing a good instrument one notices a large quantity of small stars: near this cluster is a rather brilliant star which is surrounded by a very faint light: this is the ninth star of Sagittarius, of seventh magnitude, according to the catalog of Flamsteed: this cluster appears in an elongated shape which extends from North-East to South-West. I observed its position during its passage of the Meridian, comparing it with the star Delta Sagittarii, and I determined its right ascension as 267d 29′ 30″, and its declination as 24d 21′ 10″ south. This star cluster could have an extension, from North-East to South-West, of about 30 minutes of arc.”
Enjoy this ancient beauty!
B&W image thanks to Palomar Observatory, courtesy of Caltech, color image thanks to N.A.Sharp, REU program/NOAO/AURA/NSF and thanks to HST and APOD.