John Frederick William Herschel, 1st Baronet (March 7, 1792 - May 11, 1871) was an English mathematician, astronomer, chemist, and experimental photographer/inventor, who in some years also did valuable botanical work. Herschel originated the use of the Julian day system in astronomy. He named seven moons of Saturn and four moons of Uranus. He made many contributions to the science of photography, and investigated color blindness and the chemical power of ultraviolet rays. Herschel wrote many papers and articles, including entries on meteorology, physical geography and the telescope for the Encyclopedia Britannica. He also translated The Iliad of Homer. He invented the actinometer in 1825 to measure the direct heating power of the sun's rays, and his work with the instrument is of great importance in the early history of photochemistry. He died in 1871 at the age of 79. He was given a national funeral and buried in Westminster Abbey.