NGC 6520 and the Ink Spot Nebula B86

NGC 6520 star cluster and dark nebula B86

Star Cluster NGC 6520

NGC 6520 is a well defined open star cluster that stands out from the dense background of Milky Way stars near the heart of our galaxy in the constellation Sagittarius. This cluster of stars is relatively close to us as compared with the stars forming the center region of the galaxy. The cluster is about 5,000 light-years from our solar system, while the galactic center is five times further away. NGC 6520 is composed of a number of stars between magnitude 10 and 13. In an 8-inch amateur telescope, about 30 stars in the range of magnitudes 10 to 11 may be seen tightly compressed into a circle with a diameter of only about 4 arc-minutes.

Dark Nebula B86

Not every nebula is seen as a glowing cloud of ionized gas or is illuminated by reflected light from a nearby star. NGC 6520 is tightly paired with a dark nebula that may be seen by virtue of the fact that the cloud of gas and dust forming the nebula blocks the light from stars in the background.

Barnard 86 is also sometimes called the Ink Spot Nebula. It is a dark nebula that is clearly defined as a starless, irregular form against the backdrop of the myriad of faint stars in the Milky Way. This is one of the sky's most distinct dark nebulae. The nebula is a Bok globule located about 500 light-years from us. A Bok globule is a compact dark nebula named after Dutch-American astronomer Bart Bok (1906-1983) who was the first to recognize and correctly characterize them. Dust makes up about one percent of these clouds by mass. The rest of the nebula is largely made up of cold gas. This dark cloud of dust appears to be collapsing, and perhaps will some day in the distant future form a new star. In this image, on the opposite side of the nebula from the open star cluster, an orange (spectral class K4III) star on the western edge of the dark nebula provides a 7th magnitude beacon to accent the view in superb fashion.

This is a composite RGB color CCD image taken from my backyard with an SBIG ST-8E CCD using a CFW-8 color filter wheel. The scope was a Takahashi FCT-150 refractor on an NJP Temma mount.

NGC 6520
Constellation: Sagittarius
RA: 18h 03m 37.3s Dec: -27d 54' 03"
June 10, 2003
Image by Sid Leach
Scottsdale, Arizona

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