FREDERICK WILLIAM HERSCHEL DISCOVERS ENCELADUS

Today, The Grandma has received the wondeful visit of one of her closest friends, Joseph de Ca'th Lon.

Joseph loves Astronomy and they have been talking about William Herschel, the German-British astronomer, who discovered Enceladus, a new moon of Saturn, on a day like today in 1789.

Frederick William Herschel, in German Friedrich Wilhelm Herschel, 15 November 1738-25 August 1822) was a German-British astronomer and composer. He frequently collaborated with his younger sister and fellow astronomer Caroline Herschel.

Born in the Electorate of Hanover, William Herschel followed his father into the military band of Hanover, before emigrating to Great Britain in 1757 at the age of nineteen.

Herschel constructed his first large telescope in 1774, after which he spent nine years carrying out sky surveys to investigate double stars. Herschel published catalogues of nebulae in 1802 (2,500 objects) and in 1820 (5,000 objects). The resolving power of the Herschel telescopes revealed that many objects called nebulae in the Messier catalogue were actually clusters of stars.

On 13 March 1781 while making observations he made note of a new object in the constellation of Gemini. This would, after several weeks of verification and consultation with other astronomers, be confirmed to be a new planet, eventually given the name of Uranus. This was the first planet to be discovered since antiquity, and Herschel became famous overnight. As a result of this discovery, George III appointed him Court Astronomer. He was elected a Fellow of the Royal Society and grants were provided for the construction of new telescopes.

Herschel pioneered the use of astronomical spectrophotometry, using prisms and temperature measuring equipment to measure the wavelength distribution of stellar spectra. In the course of these investigations, Herschel discovered infrared radiation. Other work included an improved determination of the rotation period of Mars, the discovery that the Martian polar caps vary seasonally, the discovery of Titania and Oberon (moons of Uranus) and Enceladus and Mimas (moons of Saturn). Herschel was made a Knight of the Royal Guelphic Order in 1816.

He was the first President of the Royal Astronomical Society when it was founded in 1820. 

On 25 August 1822, Herschel died at Observatory House, Windsor Road, Slough, and his work was continued by his only son, John Herschel.

Herschel was born in the Electorate of Hanover in Germany, then part of the Holy Roman Empire, one of ten children of Isaak Herschel and his wife, Anna Ilse Moritzen, of German Lutheran ancestry. His ancestors came from Pirna, in Saxony. Theories that they were Protestants from Bohemia have been questioned by Hamel as the surname Herschel already occurred a century earlier in the very same area that the family lived in.

More information: Herschel Museum of Astronomy

Enceladus is the sixth-largest moon of Saturn and the 19th-largest in the Solar System. It is about 500 kilometers in diameter, about a tenth of that of Saturn's largest moon, Titan. It is mostly covered by fresh, clean ice, making it one of the most reflective bodies of the Solar System. Consequently, its surface temperature at noon reaches only -198 °C (75.1 K; -324.4 °F), far colder than a light-absorbing body would be. Despite its small size, Enceladus has a wide variety of surface features, ranging from old, heavily cratered regions to young, tectonically deformed terrain.

Enceladus was discovered by William Herschel on August 28, 1789, during the first use of his new 1.2 m telescope, then the largest in the world, at Observatory House in Slough, England.

Its faint apparent magnitude (HV=+11.7) and its proximity to the much brighter Saturn and Saturn's rings make Enceladus difficult to observe from Earth with smaller telescopes. Like many satellites of Saturn discovered prior to the Space Age, Enceladus was first observed during a Saturnian equinox, when Earth is within the ring plane. At such times, the reduction in glare from the rings makes the moons easier to observe.

Prior to the Voyager missions the view of Enceladus improved little from the dot first observed by Herschel. Only its orbital characteristics were known, with estimations of its mass, density and albedo.

More information: NASA

Saturn seems to have impressed
the seal of melancholy on me from the beginning.

Marsilio Ficino