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Astronomy with an online telescope

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Described image
Figure 3 The HR diagram showing the main sequence. The letters at the top indicate the spectral class of the stars, with O and B representing the brightest and hottest stars, and K and M at the other end representing the faintest and reddest stars. The Sun, indicated with the yellow circle, is a G-class star with average brightness and temperature. Temperatures on this diagram are in Kelvins (K).

 2.3 Understanding the main sequence