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Cambridge A-Level·Physics·Cambridge AS & A Level Physics

Astronomy & Cosmology

14 min read

Standard candles and luminosity, stellar radii via Wien's law and Stefan's law, the Doppler redshift of galaxies, Hubble's law and the age of the Universe.

Luminosity and standard candles

The luminosity LLL of a star is the total power it radiates (W). The radiant flux intensity FFF received at distance ddd obeys an inverse-square law:

F=L4πd2F = \dfrac{L}{4\pi d^2}F=4πd2L​

A standard candle is an astronomical object of known luminosity (e.g. a Type Ia supernova). By measuring its flux and using the equation above, its distance can be found.

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