Henrietta Leavitt’s Star Yardstick
Written by Studio AM.
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Henrietta Swan Leavitt studied star photographs at the Harvard College Observatory in the early 1900s. She recorded how bright stars looked on glass plates. Some stars grew brighter and dimmer in regular cycles.
Leavitt compared these variable stars in the Small Magellanic Cloud. They lay in the same distant star system, so their distances from Earth were roughly similar. She found a pattern: among those Cepheid variables, longer cycles went with greater true brightness.
Later astronomers calibrated this relationship. By timing a star’s cycle, they could infer its true brightness, the light it gives off. Comparing true brightness with apparent brightness helped them estimate distance. Her work did not measure every distance by itself. It supplied a reliable step that other observations could build upon. Leavitt’s patient measurements gave astronomy a powerful new yardstick for the universe.
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Questions
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Question 1 of 4
What is the main idea of the biography?
The answer is B: Leavitt found a link between a star's cycle and brightness that helped astronomers estimate distance.
The passage centers on Leavitt’s period-brightness relationship and explains how later astronomers could use it to infer distance.
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Question 2 of 4
Why was the Small Magellanic Cloud useful for Leavitt’s comparison?
The answer is C: Their similar distances made brightness comparisons more useful.
Since the stars lay together in one remote system, differences in their observed brightness could be compared with less distance variation.
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Question 3 of 4
What does “calibrated” mean in this passage?
The answer is D: Set the relationship against known measurements so it could give useful values
Later astronomers needed to connect Leavitt’s relationship to known values before applying it as a distance-measuring tool.
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Question 4 of 4
What kind of stars did Leavitt study that repeatedly brighten and dim?
The answer is A: Variable stars
The second paragraph calls the repeatedly brightening and dimming stars “variable stars.”
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