# Measuring distance to cepheid variable star

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#1
Hello,

So if you have a cepheid variable star the radiation flux will periodically vary between maxima and minima. The greater the luminosity, the greater the time period for the varying radiation flux. Thus, using this relationship, if you have a graph of radiation flux against time, you can determine the time period of the varying radiation flux and therefore work out the star's luminosity. Using F=L/4πd^2 to work out the distance from Earth to the star, all you now need is the radiation flux of the star as measured from Earth. This is the part I do not understand. If the radiation flux is periodically varying, then how do you know which value to choose?

Thanks a lot
0
6 years ago
#2
You can take an average
http://sci.esa.int/education/35616-s...odylongid=1673

(uses a different distance formula based on apparent and absolute magnitude)
1
#3
(Original post by Joinedup)
You can take an average
http://sci.esa.int/education/35616-s...odylongid=1673

(uses a different distance formula based on apparent and absolute magnitude)
Oh, so you just find the average intensity from the intensity-time graph right?

Thanks
0
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