Norman Robert Pogson

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Asteroids discovered: 8
42 Isis	May 23 1856
43 Ariadne	April 15 1857
46 Hestia	August 16 1857
67 Asia	April 17 1861
80 Sappho	May 2 1864
87 Sylvia	May 16 1866
107 Camilla	November 17 1868
245 Vera	February 6 1885

Norman Robert Pogson (born March 23, 1829 in Nottingham – died June 23, 1891) was an English astronomer.

By the time he was 18 years old, he had computed the orbits of two comets. He became an assistant at Radcliffe Observatory in Oxford, England in 1851. In 1860 he travelled to Madras, India, becoming the government astronomer. At the Madras Observatory he produced the Madras Catalogue of 11,015 stars. He also discovered five asteroids and six variable stars.

His most notable contribution was to note that in the stellar magnitude system introduced by the Greek astronomer Hipparchus, stars of the first magnitude were about a hundred times as bright as stars of the sixth magnitude. His suggestion in 1856 was to make this a standard, so each decrease in magnitude represented a decrease in brightness equal to the fifth-root of 100 (or about 2.512). The Pogson Ratio became the standard method of assigning magnitudes.

The magnitude relation is given as follows:

$m\_\{2\}\; -\; m\_\{1\}\; =\; -2.5\; log\_\{10\}\; (L\_2\; /\; L\_1)$

where m is the stellar magnitude and L is the luminosity, for stars 1 and 2.

In 1868 and 1871, Pogson joined the Indian solar eclipse expeditions.

During his career he discovered a total of eight asteroids and 21 variable stars. He headed the Madras Observatory for 30 years until his death.

Honours

The following celestial features are named after him:

• Asteroid 1830 Pogson.
• Pogson crater on the Moon.

References

• Magnitudes of Thirty-six of the Minor Planets for the first day of each month of the year 1857, N. Pogson, MNRAS 17 pp 12 1856 in which Pogson first introduced his magnitude system

Links

• Norman Robert Pogson - Irineu Gomes Varella (Portuguese)

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