ASTR 114 Lecture Notes - Lecture 14: Apparent Magnitude, Richter Magnitude Scale, Horse Length
17 Apr 2017
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Lecture 14: stellar brightness, magnitudes, mass and radii. Luminosity: amount of power a star radiates, measured in watts (joules/sec). Apparent brightness: amount of starlight that reaches earth (watts/m2). The apparent brightness of a star depends on both distance and luminosity. Therefore, two stars that appear equally bright might be a closer, dimmer star and a farther, brighter star. The relationship between luminosity and apparent brightness depends on distance, giving the equation: We can determine a star"s luminosity if we can measure its distance and apparent brightness: The most luminous stars are 106 times more luminous than the sun (106 lsun), and the least luminous stars are 10-4 lsun. Magnitudes are a way of assigning a number to a star so we know how bright it is; this is similar to how the richter scale assigns a number to the strength of an earthquake.
