Lecture19

Lecture19 - Previous Lecture galaxy classification system...

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Unformatted text preview: Previous Lecture galaxy classification system galaxy types & definitions contents of elliptical and spiral galaxies motions in elliptical and spiral galaxies light distribution in elliptical and spiral galaxies dark matter in galaxies M/L ratio The Cosmic Distance Scale Distance determination is crucial to understanding galaxies and cosmology Distances are hard to determine accurately Local distance estimators determining the astronomical unit radar ranging, spacecraft telemetry trigonometric parallax limited range main sequence fitting only star clusters spectroscopic parallax limited accuracy Standard Candles If you know the intrinsic luminosity of an object, then its apparent brightness gives its distance Main sequence stars and Cepheids are examples not all Cepheids are identical, but P-L relation allows you to determine each Cepheids luminosity Measuring larger extragalactic distances is basically a search for brighter standard candles Not-so-good Standard Candles H II regions globular clusters brightest stars planetary nebulae brightest cluster galaxies Cepheid Variable Stars radial pulsations in giant stars...
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Lecture19 - Previous Lecture galaxy classification system...

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