Discoveries made by Sir William Herschel

William Herschel has a remarkable record of scientific discoveries. The following list is far from complete:

March 13^th 1781: the discovery of the Planet Uranus

1782-1821: the discovery that some double stars are not optical doubles, but instead binaries that are orbiting their common centre of gravity. This was the first demonstration that Newton’s laws of gravitation applied outside the solar system.

Over this time he published various catalogues of double stars that he had found containing many hundreds of systems.

1783: the discovery of the peculiar solar motion and the Solar Apex.

October 28^th 1783: the discovery of NGC 7184 (Herschel II.1), a galaxy in Aquarius.

1785: publication of the first accurate description of the shape of the Milky Way galaxy.

1783-1802: discovered and catalogued 2500 new nebulae (many of them galaxies) and star clusters. The first 1000 discoveries were made in just 18 months.

January 11^th 1787: the discovery of the satellites Titania and Oberon of Uranus

1788: the discovery that the atmosphere of Mars is very thin. His observations of the occultation of a star by Mars showed that the star only flickered and faded when extremely close to the limb of the planet, hence the planet’s atmosphere had to be tenuous.

August 28^th 1789: the discovery of the satellite Enceladus of Saturn (on the occasion of the first light of his new 1.2-m (48-inch) reflector, the largest telescope in the world for 50 years).

September 17^th 1789: the discovery of the satellite Mimas of Saturn

1798: first description of the properties of stellar spectra of different types.

1801: the discovery of infrared radiation.

1802: Coined the term “asteroid” for the Minor Planets.

Uncertain date: the discovery that an unfilled telescope aperture could be used to give higher resolution. This discovery has been applied to interferometry and has become a fundamental tool of modern astronomy.

1821: at the age of 83 he published the final supplement of his catalogue of double stars with a final list of 145 doubles.

William Herschel’s sister, Caroline, his faithful helper throughout his observational programme, started to observe of her own right in 1783 using a telescope that he had given to her. With this telescope Caroline Herschel discovered 6 comets between 1786 and 1797, including two in four months between January and April 1790.

In 1788 William Herschel married a widow in Slough, now a dormitory town for London, where he had set up his home for the rest of his life. Their son, John, later Sir John Herschel, born in 1792, became a famous astronomer in his own right, who also made many discoveries.