11.7.2007 Astronomy notes

11.7.2007 Astronomy notes - -Brightness depends upon...

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11.7.2007 – astronomy Stellar distances Distance = baseline / angle = 206,265 AU / p[arc sec] = 1 pc / p[arc sec] 1 pc = 206,265 AU P = theta / 2 Proxima centauri: p = 0.76” D = 1 / 0.76 pc = 1.3 pc = 4.3 ly = 270,000 AU Stellar Motions - Radial and transverse velocities o Barnard’s star 227” / 22 years = 10.3” per year o Gliese 710 Currently at 20 pc In 1 million years, 0.3 pc Luminosities and Magnitudes Luminosity = energy per unit time Brightness = energy flux = energy / time / area
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Unformatted text preview: -Brightness depends upon distance-Luminosity is the same, regardless of distance and what we observe with our eyes-Brightness is proportional to luminosity / distance 2 o B = L / 4D 2 Magnitude System-Hipparchus: 1 6. Lower numbers mean brighter-5 magnitude difference factor of 100 in brightness apparent magnitude-1 magnitude different = 100 1/5 = 2.5 factor in brightness-Absolute magnitude is as if everything were at 10 pc...
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