On Starts With a Bang, Ethan Siegel explains that although we see the full range of spectral classes in the night sky—from cool red M stars to blazing blue O's—75% of nearby stars "are the reddest, coolest, M-class stars, including the closest star to us." Only 4.2 light-years away, Proxima Centauri "is invisible even with binoculars, and even with dark skies, a small, 3" telescope would unable to find it." Yet O and B class stars, despite being much rarer and much more distant, are so luminous that they can't be missed. Brightness can be deceiving—even when looking at entire galaxies and…
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