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11.1 Properties of Stars.docx

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Natural Science
NATS 1740
Patrick Hall

11.1 Properties of Stars Parallax The apparent shift in position of a nearby object against a background of more distant objects  Apparent positions of nearest stars shift by about an arcsecond as Earth orbits Sun.  Parallax is measured by comparing snapshots taken at different times and measuring the shift in angle to star.  The smaller is the parallax shift, the greater is the distance to the star. Luminosity Total amount of power a star radiates (energy per second, measured in Watts) (Apparent) Brightness Amount of power per area that reaches Earth 2 (energy per second per square meter =Watts/m ) Inverse square law the equation of relationship between apparent brightness and luminosity Luminosity = Brightness / [4 π (distance) ] 2  The light from any star is spread out over a sphere surrounding the star and the luminosity passing through any sphere centered on the star is the same.  The Sun and Alpha Centauri give off about the same amounts of light, but
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