is a high velocity cloud
gas located in the constellation Aquila
at Galactic coordinates l
= 39°, b
= −13°. The cloud was discovered in 1963 by Gail Bieger
Smith, who was an astronomy student at Leiden University
in the Netherlands. Smith's cloud has a mass of at least one million solar masses
and measures long by wide in projection. The cloud is between and 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.