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Lecture

Astronomy Lecture 39

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Department
Astronomy
Course
ASTR 100
Professor
Govindrajan
Semester
Fall

Description
Astronomy Lecture 39 12/4/13 Cosmology Part I Intro 1. All galaxies show Doppler shifts a. Virgo has H and K which is calcium 2. Distances to Galaxies a. Astronomers look for standard candles b. Harlow Shapley and Edwin Hubble started with Cepheid and RR lyrae  variable stars i. Depending on pulsation period the absolute brightness could be  determined ii. A picture could show the apparent brightness 1. This allowed them to use an equation  a. Apparent brightness­ Absolute Brightness +5/5=  log10 i. (m­M +5/log10d) c. Today many other methods are used as well: Type Ia supernovae brightest  stars in a galaxy, globular clusters and the Tully­Fisher method: The  brightness of a spiral galaxy is related to its rotational velocity 3. Fundamental property of space time a. 1923/24­ Edwin Hubble measures distances to galaxies i. Andromeda was one of the first b. 1927­ Lemaitre plots velocity & distance c. 1929­ Hubble does the same thing d. 1929­ Hubble publishes the velocities – distance relation and attaches his  name to it e. 1931­ Einstein and Hubble in Pasadena announce: The Universe is  expanding i. credit shared­ Slipher, Lemaitre, Robertson, Friedman and de Sitter 4. V=H  d0means: Space is Expanding a. Two possible ways to describe it: i. Coins taped to balloon WITH ants walking on balloon ii. Raisins embedded in a cake b. Balloon expands or the cake expands. i. The coins each keep their sizes, but they spate away and grow  farther apart as the balloon or cake expand c. The balloon or cake expands uniformly, bu
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