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by Michael Erlewine

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"Baade, Walter"

Baade, Walter [Astro*Index]

(1893-1960) German-American astronomer.

In 1942, during the wartime blackout of Los Angeles, he made his detailed study of the Andromeda galaxy with the 100- inch telescope at Mount Wilson. For the first time, he was able to resolve some of the stars in the inner regions of that galaxy. He separated the stars into two sets, based on their structure and history: Population I, the bluish stars near the edges; and Population II, the reddish stars of the interior. After W.W. II, when the 200-inch telescope at Mount Polomar became available, he continued his efforts, and located over 300 Cepheids in the Andromeda galaxy. Although Cepheids were found in both Populations I and II, the period-luminosity curve of Shapley and Leavitt worked only for Population II. Thus, in 1952, Baade derived a new period-luminosity curve, with the result that our determination of the dimension of Andromeda galaxy was increased from 800,000LYs (light-years) to over 2,000,000LYs. Similarly, other dimensions had to be increased; the net result was an increase in the volume of the entire universe by a factor of 20. Recalculation of the "big bang" placed it at 5 or 6 billion years ago. (This is a reasonable figure for our solar system, although the universe may be still older.)

 

See also:
♦ Period-luminosity Relation ♦ Cepheid Variable

 

Astro*Index Copyright © 1997 Michael Erlewine

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