Anyone who has studied astronomy knows that for thousands of years the only known planets other than Earth were Mercury, Venus, Mars, Jupiter and Saturn. In 1781, William Herschel discovered Uranus, and the quest for other unseen planets began. It was only one of his many achievements.

Early Years

Born Friedrich Wilhelm Herschel in Hanover, Germany, in the year 1738, he was the second son of Isaac Herschel and his wife Ilse. Isaac was an accomplished oboist and, like his father, William also became a musician of some repute and skill. William remained close to his youngest sister Caroline, a relationship they maintained for the rest of his life. Caroline herself became a good musician and noted astronomer.

In 1753, William began playing in the Hanoverian Foot Guards Band. In 1756 he came to England, where he found work as a musical copyist in London. He followed this with a stint as a choirmaster in Halifax, and then in the year 1766, with some time as the organist at the Octagon Chapel in Bath. In 1780, he also became the director of the Bath Orchestra, and conducted some of his original music in the Pump Room. Between 1759 and 1770, Herschel wrote 18 symphonies for small orchestra, six symphonies for large orchestra and numerous other works.

An Astronomical Start

Self-taught in science and mirror-making, Herschel would eventually be recognised as one of the brightest and most dedicated of astronomers. Once he became established in Bath he purchased equipment, and with the help of his brother Alexander, William began perfecting the craft of making astronomical mirrors and telescopes. Assisted by Caroline as he watched the night sky through his telescope, he found large numbers of faint patches of light that he began to methodically catalogue. This grew into the General Catalogue of Nebulae¹.

His dedication and hard work would pay off on the night of 13 March 1781, when he discovered a celestial object and named it Georgium Sidus. We know it today by the name later given it by Johann Elert Bode². Herschel had discovered the planet Uranus.

King's Astronomer

Following this discovery, King George III granted him the post of Court Astronomer. The money that came with this post (£200 per annum) plus what he made selling telescopes of his own creation permitted him to turn his full attention to astronomy, to the grinding of his own lenses and to making better telescopes.

In 1786, he moved to Slough and built a 20' long telescope. In 1787, he used it to find the moons Titania and Oberon in orbit around Uranus. Then in 1789 he constructed the largest telescope of the day. It was 40' long and had a 48" mirror. With it, he also discovered Enceladus and Mimas circling the planet Saturn. Yet most of his nebulae were discovered with his smaller telescopes.

He continued finding deep sky objects like nebulae and galaxies, eventually finding over 2,500 of them in the next 20 years, including the Galaxy NGC 2903.

His studies beyond the solar system indicated that our sun and its solar system are moving within the galaxy in the direction of the constellation  Hercules, material he published in 1783-4.

In 1783 Herschel also recorded some stars omitted from Flamsteed's Catalogue (Historia Coelestis Britannica) and reported his findings to the Royal Society of London. Among these stars was Herschel's Garnet Star (Mu Cephei).

Discovering Infrared

Then, one day in 1800, Herschel was observing the sun and noted that certain filters became hotter than others. He decided to conduct an experiment to see if this effect was due to their colour. Setting up a mirror, a prism and some thermometers, he checked several different colours with the thermometer and he found that the temperature increased from violet to red, and that the highest temperature of all was beyond the red. He concluded that for the invisible radiation to affect the thermometer, these calorific rays must be reflected, refracted and absorbed just like visible light. It was the discovery of infrared radiation. It would be many years before the importance of this discovery became evident.

Later Life

In 1788, at the age of 50, William married Mary Pitt at Upton, and four years later they had a son John. John later became a famous astronomer in his own right.

In 1792, another musician, Joseph Haydn from Austria, visited Herschel and looked through his telescope. One can only imagine the two elderly gentlemen as they sat in an astronomical observatory discussing musical theory. Haydn must have been favourably impressed because he went home and publicised the symphonies of William Herschel.

In 1801, on a trip to Paris, Herschel met with Pierre Simon LaPlace and Charles Messier. In 1802, at a meeting of the Royal Society of London, Herschel read from his Catalogue of 500 New Nebulae, Nebulous Stars, Planetary Nebulae and Clusters of Stars; With Remarks on the Construction of the Heavens. It was in this work that he first coined the term binary star. Since that day, newer catalogues have found more than 60,000 such systems. Today, binary stars provide one of the best methods for finding the mass of celestial objects.

In 1816 William Herschel was knighted, and then in 1821 (one year before his death) Herschel became president of the Royal Astronomical Society. In 1822, at the age of 84, Herschel died, and was buried beneath the tower in the Church of St Laurence at Upton.

Recent Honours

A 40km diameter crater on the moon was named after him in 1935. Since then, craters on Mars and Mimas have also been given his name. An asteroid was named Herschel in 1960. In February 2001 a church window dedicated to him was unveiled in Upton.

In 2007, the European Space Agency launched a new orbiting infrared telescope named after him: The Herschel Space Telescope. Herschel would have been astounded to see the Christmas Tree Cluster (which he discovered) displayed by a modern infrared telescope.