Astronomy Picture of the Day

Discover the cosmos! Each day a different image or photograph of our fascinating universe is featured, along with a brief explanation written by a professional astronomer.

2000 September 3
See Explanation. Clicking on the picture will download the highest resolution version available.

Henrietta Leavitt Calibrates the Stars
Credit: AAVSO

Explanation: Humanity's understanding of the relative brightness and variability of stars was revolutionized by the work of Henrietta Swan Leavitt (1868-1921). Working at Harvard College Observatory, Leavitt precisely calibrated the photographic magnitudes of 47 stars to which all other stars could be compared. Leavitt discovered and cataloged over 1500 variable stars in the nearby Magellanic Clouds. From this catalog, Leavitt discovered that brighter Cepheid variable stars take longer to vary, a fact used today to calibrate the distance scale of our universe.

Tomorrow's picture: Aurora Persei

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Authors & editors: Robert Nemiroff (MTU) & Jerry Bonnell (USRA)
NASA Technical Rep.: Jay Norris. Specific rights apply.
A service of: LHEA at NASA/GSFC
& Michigan Tech. U.