Astronomy 1021 Lecture Notes - Lecture 12: Inverse-Square Law, Annie Jump Cannon, Photosphere
12 Dec 2018
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Document Summary
The total energy output of a str is called the luminosity which is abbreviated to l. Therefore two stars that have the same luminosity have the same totally energy output and thus are producing the same amount of energy. The solar luminosity is 3. 8 x 10^26 w. The further away a star is, the fainter is appears - brightness follows as an inverse square law. We characterize apparent brightness using the magnitude scale introduced by hipparchus. Naked eye stars scale 1 then 2 - faintest stars were scale 6. To determine total luminosity of a star we need to measure its apparent brightness and know the distance. 1 parsec = distance an object would have with a p=1 arc second (3. 26 light years) Nearby stars are very dim, while more distant stars are much brighter. Brightest stars have an energy output that is 10 billion times higher than the dimmest stars.
