ASTR Notes 4

# ASTR Notes 4 - apparent magnitude will be higher-So nearby...

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Calculating Magnitude Differences - Each magnitude is a factor of 2.5 (see page 158) - So a difference of 3 magnitudes = 2.5 x 2.5 x 2.5 = 15.6 times brighter! (Every magnitude is 2.5) - 5 magnitudes difference corresponds to a star which is 100 times brighter! - Example: A star A’s magnitude is 1.0, Star B’s magnitude is 6.0 The difference in magnitudes is 6.0 – 1.0 = 5 Magnitudes So, star B is 100 times fainter than Star A Inverse Square Law - As the light from a star goes into space it fills a larger and larger spheres. - If “r” is the radius of the sphere, - Then the area of a sphere is given by A = 4 π r^2 - The amount of light decreases with the square of our distance from the star: (Brightness of a star ~ 1/r^2) IF A CAR GETS TWICE AS CLOSE, ITS LIGHT GET 4 TIMES BRIGHTER – then 9 times Distance and Brightness - If we view a star from a double the distance, it will appear four times fainter. - Its
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Unformatted text preview: apparent magnitude will be higher. -So, nearby stars can trick us into thinking they are truly bright. -To compare stars fairly, we would need to place them all at the same distance…-We need a way to measure the intrinsic (true) brightness of stars.-The absolute magnitude does not depend on how far away it is.-It is a measure of the stars true energy output, not just its brightness as viewed from Earth. Absolute & Apparent Magnitude Apparent magnitude (m): the magnitude we see from Earth. Absolute magnitude (M): the intrinsic Magnitude (regardless of distance) Absolute mag. Is defined as the magnitude that a star would have if we viewed it at a distance of 10 pc. (parsecs) The sun’s Apparent magnitude is: m = -27 The Sun’s Absolute magnitude is: M = 4.8 If the sun were moved to a distance of 10 parsecs away, it would just barely be visible (apparent magnitude 4.8)...
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