Looking Up: The Luminosity Of Leavitt

Feb 4, 2019

Leavitt was an American astronomer (1868-1921). Though she received little recognition in her lifetime, Leavitt's discovery provided astronomers with the first "standard candle" with which to measure the distance to faraway galaxies.
Credit public domain / wikipedia

This week on Looking Up guest host Caitlyn Voige illuminates a luminary by the name of Henrietta Swan Leavitt.

When we look up into the night sky, stars look immeasurably small and distant, unchanging and everlasting. One woman, however, helped to find the distances to stars, and her name was Henrietta Swan Leavitt.

Leavitt is famous for her discoveries as a computer at the Harvard College Observatory. In 1903, she was tasked with searching for Cepheid variable stars, or stars that consistently change brightness. By 1908, she had cataloged 1777 variable stars, and had made the discovery of a lifetime. As she plotted the measurements she made, she soon found a distinct pattern. The brighter the Cepheid star, the longer its period, meaning the longer it took to cycle from its minimum to maximum brightness. With this information, she developed what is now known as Leavitt’s Law, relating the period of a star’s brightness to its energy output or luminosity. There is one more variable to the equation, though. By multiplying by the logarithm of the star’s distance, the equation could be calibrated to any Cepheid variable star. Leavitt’s Law made it possible to find the distances to these stars, and her discoveries made the stars seem much further away than we thought. 

RS Pup is a Cepheid type variable star, a class of stars whose brightness is used to estimate distances to nearby galaxies as one of the first steps in establishing the cosmic distance scale.
Credit NASA, ESA, Hubble Heritage Team; Acknowledgement: Howard Bond (STScI & Penn State U.) / nasa.gov

If you’d like to take a closer look at the stars, or any of the other wonderful and amazing things in the sky, please visit csastro.org for a link to information on our monthly meetings and our free public star parties!