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Friday November 2nd.docx

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Brock University
Bozidar Mitrovic

Friday November 2 , 2012 Astronomy Lecture: Properties of stars derive from the light, which they emit (CH.8): 1) Measure the distances of starts - for nearby stars the distance is deduced from the measurement of the parallax angle - 1au/d = sin p or d= 1au/sin p = 1au/p (for small angles) - the units can be chosen such that d (in parsec (p))= 1/p (in seconds of arc (or arc seconds)) - 1pc= 3.26 LY = 3.3 LY - for the closest stars alpha-centauri p=0.76 arcseconsds - d (distance) = 1/p (parallax angle in seconds of arc) - p= 1/d Test: - p= 1/50 = 2/100 = 0.02 - larger parallax angle the closer it is to us - closer start is a-centauri A .76 seconds - step 1: d= 1/0.5 pc=2pc - step 2: 1 pc= 3.3 LY - d= 2x3.3 LY= 6.6 ly - p = 160 LY/3.3 LY PC = 50 - d = 50 pc = 50pcx 3.3 = 160 LY Monday November 5 , 2012h 2) Luminosity of a Star (as determined from its brightness and distance) - luminosity of a source L= amount of energy which it emits per unit of time (measured in watts (w)) - the luminosity of our sun L = 4x10*26 w (hydro bill would be $8x10*19/second) - energy released in explosion of 100 billion 1 megaton nuclear bombs - brightness of a source B= amount of energy received
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