Birthday of John Herschel (1792) – Double Stars and Mathematics

John Herschel, son of William Herschel, catalogued double stars and made important contributions to astronomy and mathematics. He introduced the term ‘photography’, invented the actinometer (to measure sunlight), and worked on the mathematics of least squares (Gaussian elimination). He also wrote a definitive treatise on the slide rule. His method for measuring the distance of binary star systems used the geometry of ellipses. He was a polymath who translated the Iliad and wrote a classic text on natural philosophy.