The low southern sky at this time of year features two faint constellations -- Sculptor and Fornax -- that feature two faint, nearby galaxies. Both galaxies orbit our own galaxy, the Milky Way.
Harvard astronomer Harlow Shapley discovered the galaxies in 1938. But the galaxies were so faint that he almost missed them.
Shapley was looking at a photographic plate of Sculptor when he noticed a smudge. He thought the smudge was just a fingerprint or a defect in the plate. But other pictures showed the same smudge, convincing Shapley that the object was real. A similar object appeared in the neighboring constellation of Fornax. Shapley thought both objects were exotic star clusters, with their stars spread out from one another.
In the 1940s, though, astronomers realized that both objects were actually faint, puffy galaxies of a type never seen before. Since then, astronomers have found many similar galaxies orbiting the Milky Way. The galaxies are called "spheroidals" -- they're puffy balls of stars no more than a few thousand light-years across. They're spread-out, and they have little gas with which to make new stars. Yet they seem to be the most common type of galaxy in the universe.
The Sculptor galaxy is about 300,000 light-years away, while the Fornax galaxy is about half again as far. Yet both galaxies orbit the Milky Way like two colonies in the Milky Way's galactic empire.
Script by Ken Croswell, Copyright 2008
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