PCS 181 Lecture Notes - Lecture 5: Large Magellanic Cloud, Proper Motion, Stellar Kinematics
23 Apr 2016
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Lightyear=ly: distance that light travels in 1 year, 1 ly=9. 5x1015m. Astronomical unit=au: avg distance between earth and sun. D= if is in seconds of arc ( ), then d is in parsecs (pc) D= if we multiply by 3. 26, then d is in lightyears (ly) This method is good for stars at d < 50 pc (163 ly) Hipparchus (hipparcos) of greece (2nd century bce) divided visible stars into 6 groups. W pegasi is an 8th magnitude (m=8) star. Absolute magnitude (m)=apparent magnitude (m) of star at a distance of 10 parsecs (=32. 6 ly) from us. Today"s smog and air pollution the sun would be barely visible at 10 pc from us. Luminosity, l, is total amount of energy emitted by star each second. A plot of stellar luminosity (or magnitude) vs surface temperature or spectral type. Spectral classes: o, b, a, f, g, k, m (hottest to coldest, highest to lowest mass)
