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Welcome to our Physics lesson on Surface Temperature of Stars, this is the third lesson of our suite of physics lessons covering the topic of Stars, you can find links to the other lessons within this tutorial and access additional physics learning resources below this lesson.
The colour of a star is an indicator of the wavelength of EM radiation it emits. Giving that the state of Sun's photosphere remains constant with time, we can use this fact to conclude that all stable stars manifest this behavior as well. In Section 19 we explained that when an object radiates constant amounts of energy, it can be considered as a black body. Stars radiate in all wavelengths but the wavelength representing the colour of a given star provides the greatest contribution in radiation. We have called it "characteristic wavelength, λm" and it plays a major role in the energy radiated by the star.
Based on the Wien's Law, we have for the relationship between the characteristic wavelength and temperature of a black body:
where b = 2.898 × 10-3 m · K is a constant (Wien's constant).
It is obvious that temperature and wavelength are inversely proportional to each other. This means a star having a blue colour is hotter than a red colour star because wavelength of EM radiation decreases from red to violet (blue is just before violet in the spectrum of light colours).
The above reasoning forms the basis of chromatology mentioned in the first paragraph of this tutorial.
What is the surface temperature of a star which has a pure green appearance when viewed from Earth? The wavelength of pure green light is 530 nm.
Clues:
Applying Wien's Law
we obtain the temperature of the given star:
You have reached the end of Physics lesson 22.4.3 Surface Temperature of Stars. There are 5 lessons in this physics tutorial covering Stars, you can access all the lessons from this tutorial below.
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