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Pogson's Ratio

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Pogson's ratio is the constant

100^(1/5)=10^(2/5)=2.511886431...

(OEIS A189824) appearing in the definition of the astronomical magnitude (brightness) scale. This scale is based on the practice dating back to the Hellenistic Greeks of dividing the brightness of visible stars into six magnitudes, with the brightest stars being called first magnitude and the faintest visible stars sixth magnitude. Pogson (1856) systematized this system by defining a first magnitude star to be 100 times as bright as a sixth magnitude star using a logarithmic scale, thus making each magnitude 100^(1/5) times as bright as the previous one. This system remains widely adopted by astronomers today.

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References

Pogson, N. "Magnitudes of Thirty-Six of the Minor Planets for the First Day of Each Month of the Year 1857." Monthly Not. Roy. Astron. Soc. 17, 12-15, 1856.Sloane, N. J. A. Sequence A189824 in "The On-Line Encyclopedia of Integer Sequences."

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Pogson's Ratio

Cite this as:

Weisstein, Eric W. "Pogson's Ratio." From MathWorld--A Wolfram Resource. https://mathworld.wolfram.com/PogsonsRatio.html

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