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Sir William Herschel

Sir William Herschel

1738-1822

Friedrich Wilhelm Herschel was born in Hanover on 15th November 1738. He moved to London in 1756, learned English quickly and chose to go by the name Frederick William Herschel. In 1788, Herschel married Mary Pitt at St Laurence’s Church, Upton, and they had a son, John Frederick William.

 

The Musician

Herschel was a talented musician and composer and he played in Charles Avison’s Newcastle orchestra. He was later head of the Durham Militia band 1760-61, organist of the Octagon Chapel, Bath, and Director of Public Concerts for the town. Herschel composed a total of 24 symphonies and many concertos although much of his work is lost or forgotten.

Some representative musical instruments

 

The Astronomer

Herschel spent his spare time working on astronomy and mathematics. In 1774, with the help of his sister Caroline who was an astronomer in her own right, Herschel began a systematic and survey of the night sky. In 1781, using a 6 inch diameter 7 foot focal length telescope in the back garden of his house in Bath, he noticed an object that he initially thought it to be a comet.

 

Russian Academic Anders Lexell computed the orbit of the object and found it to more probably be a planet. Herschel agreed and that it must be beyond the orbit of Saturn. Herschel called the new planet the Georgian star (Georgium Sidus) after King George III until the name Uranus was universally adopted.

A recreation of Herschel’s workbench in his house in Bath

 

In 1782, Herschel was appointed ‘The King’s Astronomer’ and he and his sister subsequently moved to Datchet near Slough in 1782. In June 1785, William and Caroline moved to Old Windsor but in 1786 they settled in a new residence on Windsor Road in Slough where William would live the rest of his life. Caroline moved to a separate residence when William married but continued work as his assistant.

 

Herschel built his own telescopes and made more than 400 telescopes. On one occasion he was recorded by his sister as having spent up to 16 hours continuously polishing a primary mirror. His most famous telescope was the reflecting telescope that he erected in 1789 in the back garden of Observatory House, his home in Slough. It had a 49in diameter primary mirror and a 40ft focal length.

 

William Herschel built the Great Telescope, the largest in the world in its day, on the lawn of his home in Windsor Road Slough in 1789. The 49 inch reflector, which he cast and polished himself, weighed over a ton and the telescope had a 40 foot focal length. Using the telescope he discovered two satellites of Saturn, the rotation of Saturn’s rings, the motion of binary stars and gained an understanding of the Milky Way. The telescope stood for 50 years until 1839 when William’s son John demolished it as the woodwork had become rotten.

This treadle lathe was presented to Herschel by King George III at around the time that the astronomer moved to Datchet.

 

Other discoveries

Herschel discovered four new moons in the Solar System and observed some 2,000 nebulae and star clusters and recorded them in The General Catalogue of Nebulae. He also catalogued 145 double stars. He also discovered that Polaris, or the Pole Star, was a double star which was later named Polaris B. Much later it was discovered that there is actually a third star in the system.

Herschel’s major astronomical discoveries

 

Object

type

Near sky feature

Date

Telescope

Notes

Polaris B

star

Ursa Minor

1785

6in/7ft reflector

430 light years from Sun

Uranus

planet

-

13 Mar 1781

6in/7ft reflector

1·8 billion miles from Sun

Cone Nebula

Monoceros

26 Dec 1785

Uncertain

2,700 light years from Sun

Oberon

moon

Uranus

11 Jan 1787

Uncertain

2nd largest of Uranus

Titania

moon

Uranus

11 Jan 1787

Uncertain

Largest of Uranus

Eskimo Nebula

Gemini

17 Jan 1787

Uncertain

2,870 light years from Sun

Enceladus

moon

Saturn

28 Aug 1789

49in/40ft reflector

6th largest of Saturn

Mimas

moon

Saturn

17 Sep 1789

49in/40ft reflector

21st largest in Solar System

 

Along with his 6in diameter 7ft focal length telescope, Herschel also used a 12in diameter 20ft focal length telescope and an 18·7in diameter 20ft focal length telescope. The larger the diameter the brighter the image and the longer the focal length the greater the magnification. It is most likely that the more distant objects were found using the larger telescopes but the author could not find with certainty which specific telescope was used on certain discoveries.

Herschel measured the axial tilt of the planet Mars and discovered that its ice caps changed in size which indicates seasons on the planet. Herschel was also the first to realize that the solar system is moving through space and understood the structure of the Milky Way concluding that it was disk-shaped.

 

He was the first to have some real appreciation of the enormity of the universe, and an understanding of the concept of light years. In 1871 he wrote:

'I have observed stars of which the light, it will be proved, must take two million years to reach the Earth.’

It took 100 years for this principle to be proved but proved it was.

 

In 1800, he was using filters and prisms and he discovered that heat was being produced beyond the visible red end of the spectrum. He had, by accident, discovered infra-red radiation.

 

In memoriam

Photo: © Dennis Flint - used with kind permission

Sir William Herschel died at Observatory House on 25th August 1822 and he was laid to rest at St Laurence’s Church, Upton, on 7th September 1822. There is an epitaph to him in the church, as well as a beautiful stained-glass window depicting the sun, moon and the planets that were known in his lifetime. Herschel is also shown using his telescope.

 

There is a monument in Herschel Street, Slough, close to where the 40 foot telescope was positioned. The last surviving residence Herschel occupied is 19 New King Street, Bath, which is now the William Herschel Museum.

1981 postage stamp from the République du Mali commemorating the 200th anniversary of the discovery of the planet Uranus

The Herschel Museum of Astronomy

The museum is very charming and styled much as it would have been when Herschel lived there. It has a collection of musical and astronomical instruments and a workshop with the kind of tools that Herschel used to make his telescopes. Upstairs is a selection of musical instruments that he would have played and a collection of astronomical instruments. There is also a small cinema running a 10 minute loop about the Herschels.

 

The Herschel Museum of Astronomy 19 New King Street, Bath, BA1 2BL

My name is Gary Flint. To make comments on the contents of this website please click below:

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