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temperatures of stars [Q&A]


Sathwika of SDM PU College asks, how do we measure the temperature of stars?

Different parts of a star are at different temperatures. The core reaches billions of degrees, and the corona, millions. But usually what people mean when they say temperature is the temperature at the surface, the photosphere, where the star becomes transparent to the photons coming up from the interior.

By the time the energy that is released in the fusion going on in the core gets to the photosphere, it is heavily thermalized by innumerable scatterings, so the spectrum that results is a very good approximation to a Blackbody spectrum. Such a spectrum has a characteristic shape, with the location of the peak wavelength inversely correlated to the temperature, with a proportionality constant b=2.89798 107Å K. So if the spectrum can be measured, the temperature can be estimated. The spectrum is usually measured in broadband filters than span the visual range and sometimes extend into the near infrared.