Pogson , Norman Robert

(1829–1891) British astronomer

Pogson, who was born at Nottingham, started his career in 1852 as an assistant at the Radcliffe Observatory in Oxford. While there he discovered four new asteroids: Amphitrite in 1854, Isis in 1856, and Ariadne and Hestia in 1857. He was to discover nine in all, including the first to be discovered on the continent of Asia and consequently called Asia (1891).

In 1860 he was appointed government astronomer at Madras. He remained in India for the rest of his life, conscious of the enormous amount of observational work that could be done there. He constructed star catalogs and a variable star atlas while there.

His most lasting achievement was the introduction of Pogson's ratio. It had been realized that the average first-magnitude star is about a hundred times brighter than stars of the sixth magnitude. He therefore proposed that this interval should be represented by five equal magnitudes, that is, one magnitude would equal ⁵√100, which equals 2.512. This means that stars of increasing magnitude are roughly 2.5 times brighter. The system has survived in the form proposed by Pogson more than a century ago.