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Eclipsing variables.

Early on, a few stars had been noticed that were variable; that is, had light that dimmed and brightened instead of remaining constant.

The first variable star to be discovered was Omicron Ceti. In 1596 the German astronomer David Fabricius (1564-1617) noticed its changing light intensity.

The star was eventually named Mira (from a Latin word meaning "wonderful") by a German astronomer, Johannes Hevel, known as Hevelius (1611-1687).

Another variable star was noted in 1672 by an Italian astronomer, Geminiano Mantanari (1633-1687). That was Beta Persei, better known as Algol (from an Arabic word meaning "the ghoul," because it represented the head of the monster Medusa in the constellation). Algol did not vary in brightness as much as Mira did, but Algol's variations, unlike Mira's were quite regular.

In 1782 Algol was studied by a British astronomer, John Goodricke (1764-1786), a deaf-mute. To account for the regularity of Algol's variations, he suggested that it might have a dim companion that circled it in our line of sight and periodically eclipsed it, hiding most of the light.

In this, he proved to be perfectly right, but not all variable stars are eclipsing variables. Mira isn't. Its variation are so irregular that no eclipse can possibly be involved.

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Author:Asimov, Isaac
Publication:Asimov's Chronology of Science & Discovery, Updated ed.
Article Type:Reference Source
Date:Jan 1, 1994
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