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A galactic Cephid variable has a parralax of 0.002 arcseconds. What is it's distance in parsecs? A second cephid variable with the same period is 20 magnitudes fainter. What is the distance to this second star?

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Now I worked out that the distance to the former is 500pc.

Then using a flux equation I learned in lectures, I gathered that since the difference in the maginuteds is 20, one of the the stars must be 1E8 times brighter. So if we denote the second star as flux 1, the first star has flux 1E8.

But how then would I work out the distance to the second star of flux 1?