Orders of Magnitude

Published: July 18, 2021, 5 a.m.

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It doesn't make sense that stars shining at magnitude 31.5 are among the dimmest the Hubble Space Telescope can see, while one shining at 0 is one of the brightest in the sky. And objects with magnitudes below 0 are even brighter! How can the lower number mean a brighter body? It starts making sense when you understand how this measurement system got started more than 2,000 years ago.

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And find out what's happening in the sky the week of July 18 through 24, 2021.

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