Download Which has a hotter temperature, a red star or a blue star? How do

Which has a hotter temperature, a red star or a blue star? How do you know?
Note that temperature and energy are not the same thing. Also remember that all blackbodies emit
radiation at all wavelengths, regardless of temperature. The temperature just determines how much it
radiates at each wavelength. Also, E = hν is the energy ofa single photon, and ε= σT 4 is the total energy
radiated by a small piece of a black body. Both are energy, but they are not the same thing.
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Prof. Filappenko walks into class one day wearing mismatched socks: red on his right foot, and blue
on his left foot. Which of his feet is hotter? Why is your answer for this question the same/different as
whether a red or blue star is hotter?
Think about everyday life. Keep in mind that all blackbodies of a given color are about the same
temperature. Are yellow socks as hot as the sun?
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Stars A and B are next to each other in the sky, but Star A is found to be twice as hot as star B. You
measure that star A has the same total brightness (luminosity) as star B. Which star is bigger? How much
bigger?
Think about ratios. L = 4πR2 σT 4 .
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The moon takes a full month to cycle through all of its phases (29.5 days, really). If the moon is a
waining gibbous tonight, what will the phase be 2 weeks from now?
Draw the position of the Earth, Moon, and Sun when the moon appears as a waining gibbous from the
Earth. What fraction of a full cycle of phases is 2 weeks?
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