Trifid & Lagoon Nebulas
19 x 120 Seconds at ISO 1600. Hutech Idas LP Filter.
The Trifid is nearly the size of the full moon, and contains both reddish emission and bluish reflection nebulosity.
M 20 is estimated to lie about 5,200 light years away, on the far side of the same complex of nebulosity that includes the Lagoon Nebula, M 8. The Trifid's exact distance is rather uncertain, with estimates ranging from 2,200 to 9,000 light years. At the value of 5,200 light years adopted here, the Trifid spans a diameter about 10 light years across.
The Lagoon Nebula, Messier 8 (NGC 6523) is one of the finest star-forming regions in the sky, and is faintly visible to the naked eye. It is a giant glowing cloud of interstellar gas, divided by a dark lane of dust, containing a cluster of young stars (NGC 6530) that have formed from it.
The brightest parts of the Lagoon Nebula contain a feature known as the "Hourglass Nebula", discovered and named by John Herschel. This is in a region where vivid star formation is taking place, and its bright emission is caused by heavy excitation from very hot, young stars.
The nebula also contains a number of dark globules which represent collapsing clouds of protostellar material. The most prominent of these dark patches were catalogued by E. E. Barnard: B 88, a comet-shaped globule extended North-to-South in the nebula's eastern half; B 89, a smaller dark nebula near the cluster NGC 6530; and B 296, a long, narrow black patch at the nebula's south edge.
The Lagoon Nebula lies in the heart of the galaxy's Sagittarius-Carina spiral arm, but its distance is a bit uncertain. Estimates range from 4,800 to 6,500 light years, with 5,200 quoted by many sources. A 2006 study found a distance of 4,100 light years, which would make its true size about 110 x 50 light years. . The dark "Bok" globules of collapsing protostellar material have diameters of about 10,000 AU.