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The spectral class of a star tells us the temperature of the star.
The absorption spectrum of a star tells us the composition of a star as well as the temperature of a star because the intensity and presence of certain spectral lines are a function of temperature.
When absorption spectra of stars were first collected by astronomers, they were grouped together by noticing similarities such as the intensity and presence of certain spectral lines. At the time, it was not understood what variable (or variables) that determined these differences in the spectra of stars.
Later, it was learned that temperature was the variable that affected the differences in stellar spectra. After this was understood, it gave us a new technique for determing the temperature of a star.
To determine the temperature of a star: (1) collect the spectrum of the star, (2) compare it to the spectra of stars of known temperature, (3) determine the spectral class of the star, and finally (4) deduce the temperature of the star.
The spectral classes are defined as: (from Astronomy, by Zeilik)
An example spectrum for each class is shown below:
Note that each class is also broken into subclasses from 0 (hottest) to 9 (coolest) with each subclass identified by certain spectral lines. The figure above actually shows spectra for O4, B5, A0, F0, G0, K0, and M2 stars. Sun is a G2 star with a surface temperature of 5800 K.
Thus, to get the temperature of a star, astronomers use a spectrometer to record the absorption spectrum of the star. Then, a computer (or a person) compares the spectrum to a catalog of spectra in order to determine the spectral classification of the star. Because we know the temperatures of the various classes of stars, this gives the temperature of the star.
Note: to keep spammers out, the feedback form requires you to type the class name, such as PHY1050, in order to submit feedback.
Class (enter PHY1050):
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