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J B Lester

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AST 201S - Stars and Galaxies University of Toronto Mississauga Chapter 11 Summary th Essential Cosmic Evolution, 5 Edition 1. “Snapshot” approach = observe many stars at one time of their lives to capture the full range of stellar properties and lives 2. Brightnesses of stars • We observe the apparent brightness • Apparent brightness depends directly on Luminosity • Apparent brightness depends inversely on the (distance)2 apparent brightness ∝ Lum d2 • Measure distances using parallax = triangulation • Stars are many light-years from the Sun, 1 light-year is the distance traveled by light in one year = 9.46 × 10 km • Stars have a wide range of luminosities: – least luminous star = 0.0001 × L Sun – most luminous stars = 1,000,000 × L Sun • Counting stars, the Sun is slightly more luminous than the average star 3. Temperatures of stars • Find the temperature using the laws of thermal radiation (Wien’s law, Stefan- Boltzmann law) or • Find the temperature from the mixture of atoms, molecules and ions identified by their spectral line patterns • Range from 3000 K to 50,000 K • Sun (5800 K) is slightly hotter than average 4. Masses of stars rd • Use Newton’s version of Kepler’s 3 Law, 2! 3 M + M = 4π a 1 2 G p2 Observing p and a, we solve for M1, assuming we can ignore M 2 • Appl
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