101 Must-See Cosmic Objects: The Lagoon Nebula

The Orion Nebula gets tough competition for best-in-class from the Lagoon Nebula (M8) in Sagittarius. The Lagoon Nebula is visible to the naked eye on dark moonless nights as a bright spot along the Milky Way north of the beak of the Sagittarius Teapot asterism.

The Lagoon Nebula was discovered by Italian astronomer Giovanni Battista Hodierna in 1654, when he described it as a nebula. What Hodierna probably saw, however, was not what we know today as the Lagoon Nebula, but rather an embedded open star cluster separately cataloged as NGC 6523. In fact, most records of early observations refer to the open cluster without mentioning the nebula from which it originated.

William Herschel was the first to define the nebula as a separate object. In 1785 he described it as “a vast milky nebulosity divided into two parts”. Irish astronomer Agnes M. Clerke coined the nickname “the Lagoon Nebula” in her 1890 book The star system.

When we set our sights on M8, our gaze takes us some 4,100 light years away. Under dark skies, 10×50 binoculars can make out the overall oval shape of the lagoon, as well as the dark slice that bisects the nebula. Telescopes, meanwhile, reveal many of the swirling nebula’s more intricate features.

Hidden within the nebula is another star cluster: NGC 6530. Some of its young stars twinkle among the rifts in the nebulosity. If you plan on looking for it, expect to spot between two dozen and three dozen light fixtures in most backyard spotting scopes.

Many other stars are also found in the lagoon clouds. One of the brightest is Sagittarii of magnitude 69, a massive binary system comprising two extremely close O-type stars whose radiation energizes much of the nebula. Another notable star in the field is Herschel 36, a magnitude 9.5 supergiant just west of the brightest part of the nebula.


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