Smith's Cloud

Smith's Cloud is a high-velocity cloud of hydrogen gas located in the constellation Aquila at Galactic coordinates l = 39°, b = −13°. The cloud was discovered in 1963 by Gail Bieger, née Smith, who was an astronomy student at Leiden University in the Netherlands.

Properties

Using the National Science Foundation's Robert C. Byrd Green Bank Telescope, radio astronomers have found that Smith's cloud has a mass of at least one million solar masses and measures 3,000 parsecs (9,800 ly) long by 1,000 pc (3,300 ly) wide in projection. The cloud is between 11,100 pc (36,000 ly) and 13,700 pc (45,000 ly) from Earth and has an angular diameter of 10 to 12 degrees, approximately as wide as the Orion constellation, or about 20 times the diameter of the full moon, although the cloud is not visible to the naked eye.

The cloud is apparently moving towards the disk of the Milky Way at 73 ± 26 kilometers per second. Smith's Cloud is expected to merge with the Milky Way in 27 million years at a point in the Perseus arm. Astronomers believe it will strike the Milky Way disk at a 45° angle, and its impact may produce a burst of star formation or a supershell of neutral hydrogen.