Astronomy 1011A/B Lecture Notes - Lecture 16: Elliptical Galaxy, Irregular Galaxy, Cosmic Distance Ladder
28 Jun 2016
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Document Summary
Deep fields are one way to look at a lot of galaxies at once. They contain very little cool gas and often contain hot, ionized gas: irregulars do not fit either of the other categories. Spiral galaxies, elliptical galaxies, and irregular galaxies. Spiral galaxies tend to collect into groups of up to a few dozen galaxies. The distance measurement chain begins with parallax measurements that build on radar ranging in our solar system. Using parallax and the relationship between luminosity, distance, and brightness, we can calibrate a series of standard candles. The faster a galaxy is moving away from us, the greater its distance velocity. Measuring a galaxy"s distance and speed allows us to figure out how long the galaxy took to reach its current distance. Measuring hubble"s constant tells us that amount of time about 14 billion years. Which kind of stars are best for measuring large distances?. Cephid variable stars with longer periods have greater luminosities.
