3.5 Astro 1 Section 1 Professor Brandt

3.5 Astro 1 Section 1 Professor Brandt - Astro 1 Section 1...

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Astro 1 Section 1 Professor Brandt Friday March 5th 1999 Announcements: Lecture notes: Class 24 As usual it is very important to be able to measure distances on very large scales - recurring problem for astronomers. We have talked about several methods astronomers use to measure distances to cosmic objects. - parallax - spectroscopic parallax - RR Lyrae variable stars - Cepheid variable stars However not even Cepheid variable stars can be used to probe quite distant galaxies. Even with HST Cepheid variables can only be used to about 15 Mpc - not bright enough. For comparison the most distant quasar known has a distance of about 40 000 Mpc. Makes it clear we need other methods. Again we rely on standard methods. Need luminosity and apparent brightness to get distance. - P-L relation gave us Cepheid L and let us make progress. - We rely on other tricks for even larger distances. - can figure out brightest globular clusters in nearby galaxies and compare to more distant ones. Globular clusters are quite luminous so
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