How do we measure distances to astronomical objects that are too far

away to use Trigonometric Parallaxes? This first lecture of Unit 4

reviews geometric methods like trigonometric parallaxes, and then

introduces the idea of Standard Candles, and how they are used to

develop methods for deriving Luminosity Distances based on the Inverse

Square Law of Brightness. We will explore three luminosity-based

distance methods useful for studying our Galaxy and nearby galaxies:

Spectroscopic Parallaxes, Cepheid Variable Period-Luminosity Relation,

and the RR Lyrae P-L Relation. Recorded 2006 February 6 in 1008 Evans

Laboratory on the Columbus campus of The Ohio State University.