The question is A main sequence star is barely visible at a distance of 20 pc with a certain telescope. The star subsequently(adsbygoogle = window.adsbygoogle || []).push({});

ascends the red giant branch, during which time its surface temperature drops by a factor of 3 and its radius increases by a factor of 50.

a) Determine the how luminous the star is now compared to its original luminosity, that is, determine

LRED GIANT/LORIGINAL

b) Determine how far away this star could be seen now by the same telescope.

So far, I have, L=R^2 * T^4. and that Radius is proportional to [tex]\sqrt{luminosity}[/tex]/temperature.

and Apparent magnitude - absolute magnitude = 5 log(base 10) (Distance/ 10 pc).

I am stuck at determining the radius and luminosity of the star before it ascends.

Any hints/ help would be greatly appreciated.

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# Luminosity of a star

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