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Welcome, my name is Phil, and in this video I explain how the radius of stars is calculated.

In order to calculate the radius of a star we first need to measure the temperature and apparent magnitude of the star. The temperature of the star is found by assuming stars behave as a blackbody. Here, a star emits a certain continuous spectrum according to its temperature. The apparent magnitude is measured from Earth and is how bright we see the star. The absolute magnitude (magnitude from 10 parsecs) can be found by measuring the distance to star using parallax. Once the absolute magnitude is calculated it is converted to a luminosity. It is also know that the luminosity of a star is related to its temperature and radius. Since we now know the temperature and luminosity we can work out the radius.

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