ASTR 1103 Lecture Notes - Lecture 13: Harlow Shapley, Henrietta Swan Leavitt, Delta Cephei
9 Feb 2020
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Document Summary
Cepheid variables: variable stars whose period is related to their luminosity, massive stars are larger and pulsate slower. Lower mass stars are less luminous and, being smaller, pulsate faster. Instability strip - a place on the hr diagram where stars are pulsating. Star clusters and the centre of the galaxy: globular star clusters and centre of galaxy located mostly in sagittarius and scorpius, earth is located about 26,000 lightyears from the centre of the milky way. Cepheid calibration: shapley used proper motions of stars to find distances to nearest cepheids, proper motion - rate at which a star moves across the sky (arcsec/year, calibrate - find the true value of a measurement. In 1924 edwin hubble found cepheids in the andromeda galaxy and estimated the distance to it (2. 5 million light years) Components of the galaxy: disk, central bulge, spiral arms, sphere, halo, diameter is about 80,000ly.
