The apparent brightness of a Cepheid variable star in a far-away galaxy is measured to be 640,000 times fainter compared to an equivalent star 2,000 light years away from the Sun in our Galaxy. Assuming that there is no light absorption between galaxies, what is the distance to the host galaxy of the Cepheid?
Astronomy - drwls, Sunday, November 21, 2010 at 12:59am
Use the inverse square law for brightness.
To be 640,000 times weaker, the star must be sqrt640,000 = 800 times farther way, if the two stars have the same abolute magnitude.
2000 ly x 800 = ____ light years