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Transcript
Astronomy Problems – Color Index Nov. 2011 Colors of Stars Astronomers measure the brightness of stars at three colors of light: The "U" band at 360 nm The "B" band at 440 nm The "V" band at 540 nm The "color index" of a star is defined as the magnitude in the B filter, minus the magnitude in the V filter. Color Index = B-V, where B and V refer to the magnitude of a star in those colors. Consider a star that appears red to us. Is its color index positive or negative? _________ Consider a star that appears blue to us. Is its color index positive or negative? _________ At what wavelength would you expect a star with a temperature of 10,000 K to be brightest? ______________ At what wavelength would you expect a star with a temperature of 4,000 K to be brightest? ____________ Fill in the following table. Color Bright or faint in B? Bright or faint in V V magnitude big or small? B magnitude big or small? Cool Star (4,000 K) Red Hot Star (10,000 K) Blue