Natural Science Lecture 325

Natural Science Lecture 325 - Natural Science Lecture...

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Natural Science Lecture 25/03/2008 12:00:00 Hertsprung Russel Diagram HR Diagram plots intrinsic brightness (luminosity, or absolute magnitude) vs. surface temperature (spectral type, or color) of stars. About 90% of stars lie on the “Main Sequence” of the HR Diagram. See Krauskopf and Beiser pg. 688 fig. 17-23 If stars are too far to measure distance with parallax, you use the H.R diagram. By knowing its spectral type , we can read its luminosity to find out how bright it is, then you use the following equation to find the distance. B=constant x L/d^2 B: apparent bright ness of star L: luminosity of star from HR diagram D: distance between earth and star. Cepheid Variables – sort of like lighthouses in outer space – they periodically get brighter and dimmer. Standard candles and absolute luminosity-period relation. SEE GRAPHS Henrietta Leavitt found true brightness of a Cepheid variable star is related to the period of variation in its light. Period of pulsing gives absolute brightness -> distance.
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Natural Science Lecture 325 - Natural Science Lecture...

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