Astronomy
Stars
Stellar Evolution

How is a star's color related to its temperature?

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11/03/2017

The color of a star's visible light indicates its surface temperature: a relatively cool star glows red (longer wavelength), and very hot ones glow bluish-white or even blue (shorter wavelengths).

* Blue more than 30,000 °Kelvin * Blue to blue white 10,000 to 30,000 °Kelvin * White 7,500 to 10,000 °Kelvin * Yellowish White 6,000 to 7,500 °Kelvin * Yellow 5,200 to 6,000 °Kelvin * Orange 3,700 to 5,200 °Kelvin * Red 1,000 to 3,700 °Kelvin * Brown less than 1,000 °Kelvin

* Black close to 0 °Kelvin The relationship is λmax*T=2.898*10^-3m°K Where λmax is the wavelength at which the star emits the maximum amount. So, for example for the Sun λmax = 5.1 nm Therefore T=(2.898*10^-3m°K)/(5.1*10^-9m) T=568,000 °C So as an object increases in temperature, its colour will slowly change, starting at red and progressing into blue and beyond.





A stars temperature is generally worked out by the average temperature of the photosphere.

This is not typical through out the star however.

The Solar Corona which is above the photoshere is very hot indeed, several million degrees. We normally cant see this because it does not shine in visible light. We only see this during an eclipse. It the bright band that is visible that seems to surround the moon during a solar eclipse. It is caused when matter is excited by the solar magnetic field.

Hotter still is the core. In the sun this is thought to be 10 - 20 million degrees. These temperatures are due to the pressure caused by gravity trying to compress the star. It has to be this temperature for fusion of hydrogen to take place. Once fusion starts in a young star this adds to the temperature to ensure that fusion continues.
The star's temperature is depended on the color of the star, blue is the hottest ,and red is the coolest.
the red stars are at under 3,500 K

the white and yellow stars are at 5,000 - 6,000 K

the blue and white stars are at 6,000 - 7,500 K

the blue stars are at over 25,000 K