ASTR 101 Lecture 12Outline of Last Lecture I. Measuring StarsII. Stellar ParallaxIII. Luminosity, Brightness, DistanceIV. Light and TemperatureOutline of Current Lecture I. LuminosityII. Brightness and LuminosityIII. Magnitude scaleIV. Stellar temperatureCurrent LectureChapter 11 (Review of last lecture because we had a sub)Surveying the StarsLuminosity 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 squareThe relationship between apparent brightness and luminosity depends on distance:Brightness = Luminosity / 4pi (distance)2Parallax 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) = (1001/5)m1-m2- (luminosity of star 1)/(luminosity of star 2) = (1001/5)m1-m2How 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 levelWe measure mass using gravity.Direct mass measurements are possible only for stars in binarystar
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