"How far are the spiral nebulae? How large is the universe? We cannot begin to answer these questions unless we measure the distance of heavenly objects. The breakthrough was made by Henrietta Leavitt, who was interested in a rather special class of stars, the Cepheids. The intensity of light coming from Cepheids rises and falls regularly with time... Concentrating on one of the Magellanic Clouds, she found that there was a very close relationship... The brighter the Cepheid was, the longer its period. The distance of the Magellanic Cloud is so great that the stars there can be regarded as all being effectively the same distance from the Earth. If you are in Los Angeles, everybody in Carnegie Hall is about the same distance from you. ...Suppose that a Cepheid in the cloud has a certain brightness and a period of one week. Now look at another Cepheid in some more distant galaxy. If it has the same period, we can assume it has the same intrinsic brightness, and yet it is dimmer than it should be. ...we can work out the relative distance from Earth. A star of the same intrinsic brightness that is twice as far away will be four times dimmer. ...It is slightly complicated by the effects on brightness of interstellar dust clouds, but it was a huge step forward."
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Harvard University alumniWomen scientists from the United StatesAstronomers from the United StatesHarvard University staffScientists from Massachusetts
Original Language: English
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Sources
Brian L. Silver, The Ascent of Science (1998)
https://en.wikiquote.org/wiki/Henrietta_Swan_Leavitt
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Henrietta Swan Leavitt
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