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| Clusters Nebulae Galaxies on Jun 29, 2009

The Lagoon Nebula, Messier 8

The Lagoon Nebula is the largest and brightest of a number of nebulosities in and around Sagittarius.

How to see it

The Lagoon Nebula, also known as M8 or Messier 8, is a large gas cloud within the Milky Way Galaxy, barely visible to the human eye under good conditions. It appears a few degrees above and to the right of the Teapot of Sagittarius. Visually about three times the size of the full moon, the Lagoon Nebula is the largest and brightest of a number of nebulosities in and around Sagittarius. As just a very faint patch to the unaided eye, the nebula takes on an oblong shape in binoculars. A brighter nucleus (the so-called “hour glass”) is visible on one side, separated by a dark rift, from an open star cluster on the other side. Unlike the published timed-exposure photographs, to the unaided eye the faint nebulosity appears grayish with little if any hint of color.

The Lagoon Nebula (M8) Photo by ESO/S. Guisard/S. Brunier

Although it can be seen at other times, the Lagoon Nebula is best viewed from mid-summer to mid-fall. In early May, M8 crosses the local meridian — meaning that it is highest and due south in the sky — at about 4 a.m. (Daylight Time). By July 7, it crosses the meridian at midnight. By early September it is crossing the meridian as it gets dark, making it prime for early evening observations.

Photo Credit: ESO/S. Guisard/S. Brunier

The Lagoon Nebula is widely visible throughout the populated areas of North America. However, due to its location in the sky (-24 degrees declination), observers farther south see it higher in the sky, which is better for observing. A line drawn from Phi Sag through Lambda Sag and onward approximately as far as those two stars are apart will lead the general area of M8.

History and Myth

While the fanciful name “Lagoon” might suggest a mythical origin, there is no known mythology associated directly with this interstellar cloud. The name apparently refers to the shape with the dark lane through the middle, not unlike two lagoons separated by a sandbar. While visible to the unaided eye and therefore certainly seen in antiquity, there is no known mention of it until 1654, when Sicilian astronomer Giovanni Battista Hodierna recorded his observations of the star cluster within the nebula. The area was observed by several other astronomers, including Charles Messier in 1764, after which it ultimately also became known as Messier 8, or M8, the eighth object in Messier’s catalog.

Science

M8 is about 5000 light years away, and roughly 130 light years across in the longer dimension. Composed primarily of hydrogen, much of it ionized (heated or energized) by radiation from the nearby superstar Herschel 36, M8 is known as an emission nebula. As such it also is a star-forming region, sometimes called a “stellar nursery.” There is an open star cluster, NGC 6530, of young, hot, blue stars probably only a few million years old. In addition to these young stars, there are also many dark “Bok” globules of condensing gas and dust on their way to becoming “protostars” and ultimately full-fledged stars like those already formed nearby.

The Lagoon Nebula’s approximate center position is RA: 18h 04m, declination: -24°22′

Trifid Nebula, a summer Milky Way treasure