Estimating Stellar Radius and Temperature

Edexcel A-level PhysicsSpaceLesson 6 of 18

We cannot measure the size of a distant star directly, but combining the laws from the previous lessons lets us calculate it.

Step 1, temperature: find the peak wavelength of the star's spectrum and use Wien's law, T = 2.898 × 10⁻³ ÷ λ_max.

Step 2, luminosity: measure the intensity I received at Earth and find the distance d (for example by parallax). Then L = 4πd²I.

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stefan-boltzmann law: The law stating that the power radiated per unit area of a black body is proportional to the fourth power of its absolute temperature.
parallax: The apparent change in position of a nearby object against a more distant background when viewed from two different points, used to measure stellar distance.
red supergiant: A very large, extremely luminous, cool star formed when a high-mass star's outer layers swell as its core fuses progressively heavier elements.