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Lagoon Nebula

The bright Lagoon Nebula is home to a diverse array of astronomical objects. Particularly interesting sources include a bright open cluster of stars and several energetic star-forming regions. When viewed by eye, cluster light is dominated by an overall red glow that is caused by luminous hydrogen gas, while the dark filaments are caused by absorption by dense lanes of dust. The above picture, from the Curtis-Schmidt Telescope, however, shows the nebula's emission in three exact colors specifically emitted by hydrogen, oxygen, and sulfur. The Lagoon Nebula, also known as M8 and NGC 6523, lies about 5000 light-years away. The Lagoon Nebula can be located with binoculars in the constellation of Sagittarius spanning a region over three times the diameter of a full Moon.

One of the remarkable features of the Lagoon Nebula is the presence of dark nebulae known as "globules" which are collapsing protostellar clouds with diameters of about 10,000 AU (Astronomical Units). Two distinct globules are lower- right of center. The lower of the two (shaped like a comet heading downward) is number 88 in Barnard's catalog of globules (B 88). The upper of the two (shaped like a tadpole heading left) is B 89. It is just below a cluster of bright, young stars, labeled NGC 6530, which were born of collapsing dust and gas in the nebula. Above the center and slightly to the left is a smaller tadpole-shaped globule numbered B 296.

Within the brightest part of the Lagoon Nebula (left of center), a remarkable feature can be seen, which according to its shape is called the "Hourglass Nebula." This feature was discovered by John Herschel and occurs in a region where a vivid star formation process appears to take place currently; the bright emission is caused by heavy excitation of very hot, young stars, the illuminator of the hourglass is the hot star Herschel 36 (mag 9.5, spectral class O7). Close by this feature is the apparently brightest of the stars associated with the Lagoon Nebula, 9 Sagittarii (mag 5.97, spectral class O5), which surely contributes much of the high energy radiation which excites the nebula to shine. As published in January 1997, the Hubble Space Telescope has been used to study the Hourglass Nebula region in the Lagoon Nebula M8.

The young open cluster NGC 6530 (left of center) was classified as of Trumpler type "II 2 m n" (see e.g. the Sky Catalog 2000), meaning that it is detached but only weakly concentrated toward its center, its stars scatter in a moderate range of brightness, it is moderately rich (50--100 stars), and associated with nebulosity (certainly, with the Lagoon nebula). As the light of its member stars show little reddening by interstellar matter, this cluster is probably situated just in front of the Lagoon Nebula. Its brightest star is a 6.9 mag hot O5 star, and Eichler gives its age as 2 million years. Woldemar Götz mentions this cluster as containing one peculiar Of star, an extremely hot bright star of spectral type O with peculiar spectral lines of ionized Helium and Nitrogene.

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