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Using Cepheid variable to estimate distance to galaxy watch

1. I have this question that i cant figure out, it is:

"Describe how the pulsations of Cepheid variable can be used to estimate the distance to the galaxy in which it is found"

help?
2. The problem with looking at a star in a distant galaxy is that you don't know how much light that star is putting out.
if it looks bright it could be because it's very luminous and very distant - or it could be relatively dim and quite close

Cepheids can be used as a 'standard candle' - the period of pulsation is related to their luminosity... if you measure how long the pulsations take you know how much light the star is putting out (M), you can measure the apparent magnitude from earth (m) then you can work out how distant (d) it is using the magnitude equation... m-M=5 log (d/10)
3. (Original post by Joinedup)
The problem with looking at a star in a distant galaxy is that you don't know how much light that star is putting out.
if it looks bright it could be because it's very luminous and very distant - or it could be relatively dim and quite close

Cepheids can be used as a 'standard candle' - the period of pulsation is related to their luminosity... if you measure how long the pulsations take you know how much light the star is putting out (M), you can measure the apparent magnitude from earth (m) then you can work out how distant (d) it is using the magnitude equation... m-M=5 log (d/10)
Ooohhh, thats how, thank you !!

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