Monday, March 23, 2009

March 23: Norman Robert Pogson

Norman Robert Pogson
March 23, 1829 – June 23, 1891

Norman Robert Pogson 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 traveled to Madras, India, becoming the government astronomer. At the Madras Observatory he produced the Madras Catalog of 11,015 stars.

In 1861, Pogson was appointed the government astronomer at Madras, India. He was the Director from 1861 to 1891. When he arrived he had to work under harsh conditions. He found the instruments in a bad shape and there were no proper staff to assist him. In spite of all these he began a series of observations which lasted until his death 30 year later. He was credited with 50,000 observations, most of which were published by Michie Smith after Pogson's death. During his stay in Madras he discovered several minor planets and detected large number of variable stars. He named his daughters after the minor planets he discovered. He was also well known for his work in comets and solar eclipses.

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:

m2 − m1 = − 2.5log10(L2 / L1)

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.

The Lunar crater Pogson and asteroid 1830 Pogson are named in his honor.


  1. Keep up the great work with your blog!

    By the way, March 23, 2009 is also the 15th anniversary of the discovery of comet Comet Shoemaker-Levy 9 at Palomar Observatory.

  2. Thanks, Scott. I added the Palomar discovery to the Astronomy Compendium.