N. R. Pogson

N. R. Pogson

Sir Norman Robert Pogson KBE (23 March 1829 in Nottingham – 23 June 1891 in Chennai, India) 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 eight 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 a hundred times as bright as stars of the sixth magnitude. Pogson's suggestion in 1856 was to make this a standard; thus, a first magnitude star is 1001/5 or about 2.512 times as bright as a second magnitude star. This fifth root of 100 is known as Pogson's Ratio.

The magnitude relation is given as follows:

m₁ - m₂ = -2.5 log₁₀ (L₁ / L₂)

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. In 1872, he observed an object (recorded as X/1872 X1) which he believed to be a return of Biela's Comet.

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.