who is the person?
An American astronomer.
Henrietta Swan Leavitt
Henrietta Swan Leavitt (; July 4, 1868 – December 12, 1921) was an American astronomer. 
do all stars spend the same amount of time on the main sequence The total life span can be estimated, to first approximation, as the total energy produced divided by the star's luminosity. what is main sequence? Continuous and distinctive band of stars that appears on plots of stellar color versus brightness. describe a few of its properties? Majority of stars on a typical HR diagram lie along the main-sequence curve and temperature of a star determines its spectral type mention a few variations in luminosity color? Cepheid variables, Delta Scuti variables, and Beta Cephei variables what is the first variation? A type of star that pulsates radially, varying in both diameter and temperature name a few stars from such variation? UNANSWERABLE what is the anomalous in this variation? A group of pulsating stars on the instability strip have periods of less than 2 days, but with higher luminosities. state the pulsation model in this variation? Pulsation of Cepheids is called the Eddington valve, or "κ-mechanism", where κ (kappa) is the usual symbol for the gas opacity. who proposed such a model? UNANSWERABLE who discovered such a variation of stars? Henrietta Swan Leavitt
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Henrietta Swan Leavitt [SEP] Introduction
Henrietta Swan Leavitt (; July 4, 1868 – December 12, 1921) was an American astronomer. A graduate of Radcliffe College, she worked at the Harvard College Observatory as a "computer", tasked with examining photographic plates in order to measure and catalog the brightness of stars. This work led her to discover the relation between the luminosity and the period of Cepheid variables. Leavitt's discovery provided astronomers with the first "standard candle" with which to measure the distance to faraway galaxies. After her death, Edwin Hubble used Leavitt's period-luminosity relation, together with the galactic spectral shifts first measured by Vesto Slipher at Lowell Observatory, in order to establish that the universe is expanding (see Hubble's law).