ASTR 101 Lecture 12 Outline of Last Lecture I Measuring Stars II Stellar Parallax III Luminosity Brightness Distance IV Light and Temperature Outline of Current Lecture I Luminosity II Brightness and Luminosity III Magnitude scale IV Stellar temperature Current Lecture Chapter 11 Review of last lecture because we had a sub Surveying the Stars Luminosity passing through each sphere is the same The same amount of starlight passes through each sphere The surface area of a sphere depends on the square of its radius distance from the star so the amount of light passing through each unit of area depends on the inverse square The relationship between apparent brightness and luminosity depends on distance Brightness Luminosity 4pi distance 2 Parallax and Distance p parallax angle d in parallax 1 p in arc seconds The Magnitude Scale m apparent magnitude M absolute magnitude apparent brightness of Star 1 apparent brightness of Star 2 100 1 5 m1 m2 luminosity of star 1 luminosity of star 2 1001 5 m1 m2 How do we measure stellar temperatures Level of ionization can reveal a star s temperature Absorption lines in a star s spectrum tell us its ionization level We measure mass using gravity Direct mass measurements are possible only for stars in binary star systems
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