Scouring the heavens with his sister, Caroline, Sir William Herschel discovered the planet Uranus and several moons around other gas giants. In the course of his studies of the night sky, he also compiled a catalog of 2,500 celestial objects that is still in use today. But it wasn't until his mid-30s that he began to turn his eyes to the expanse above; he started his professional life as a musician.
A musical beginning
Born in Germany as Friedrich Wilhelm Herschel, the astronomer was the son of Anna Ilse Moritzen and Issak Herschel. His father was a military musician, and young William played in the same band in his early years. In 1759, Herschel left Germany for England, where he taught music before becoming an organist.
In 1772, William's sister, Caroline, moved to England to live with her brother and train as a singer. During this time, Herschel's interest in astronomy grew significantly. He rented a small telescope, and his desire to own a larger instrument led him to the process of grinding and polishing his own mirrors.
Caroline never married, but served as his assistant until Herschel's death. She was the first woman to discover a comet, ultimately finding eight. She also discovered several deep-sky objects and was the first woman to be given a paid scientific position and to receive an honorary membership into the Royal Society.
In 1788, at the age of 50, Herschel married the widow Mary Pitt. Their son, John, was born in 1792, and followed in his father's astronomical footsteps.
Searching the skies
On March 13, 1781, Herschel noticed a small object that, over the course of several nights, was slowly moving across the sky. At first he thought he had found a comet, but further observation revealed that the object was a planet. Herschel lobbied to name the new body 'Georgium Sidus', after King George III, but it was eventually named Uranus after the Greek god of the sky. As a result of his discovery, the monarch knighted Herschel and appointed him to the position of court astronomer. The attached pension allowed him to conclude his musical career and focus his full attention on the skies.
When Herschel was subsequently elected a member of the prestigious Royal Society, he received a copy of Charles Messier's "Catalog of Nebulae and Star Clusters," a list of diverse nebulae in the night sky. The catalog piqued his interest, and he began to examine the fuzzy objects.
On Oct. 23, 1783, he began a sky survey of his own, standing on a ladder while peering through his telescope and describing the objects he saw to his sister, Caroline. By pointing the stationary telescope at a single strip of the sky, he was able to observe east-west bands over the course of the night. The next night, he would adjust his telescope to a higher or lower point and observe another parallel strip. Eventually, he examined the entire swatch of sky that could be seen over Great Britain.
Over 20 years, he observed 2,500 new nebulae and star clusters and recorded them in "The General Catalogue of Nebulae." The catalog was eventually enlarged and renamed the "New General Catalogue," and many non-stellar objects are identified by their NGC numbers. Of the 7,840 nebulae and clusters in the catalog today, 4,630 were discovered by Herschel and his son.
In 1789, Herschel finished construction on 40-foot-long (12 meters) telescope, the largest of the day. But the unwieldy instrument came with a number of problems, and Herschel tended to use the smaller, 20-foot (6-meter) telescope.
Herschel discovered several moons around the gas giants. In 1787, he discovered two moons around Uranus: Titania and Oberon. In 1789, using his larger telescope, he found Saturn's sixth and seventh moons, Enceladus and Mimas. [Meet Mimas: Saturn's Death Star Moon]
In 1800, Herschel performed a simple experiment determining the temperature of the different colors of sunlight passed through a prism. He noticed the region just beyond the red color was even higher than light in the visible spectrum, and used his measurements to deduce the presence of what is now known to be infrared radiation. The European Space Agency's infrared space observatory was subsequently named for him.
Herschel proposed the name "asteroids" for the large bodies discovered in 1801. He was elected vice president of the newly formed Royal Astronomical Society in 1820 and president the following year. His last published paper cataloged 145 double stars.
Herschel died in England on Aug. 25, 1822, at the age of 83. Craters on the moon, Mars and Mimas are named for the astronomer. The asteroid 2000 Herschel bears his name, and the symbol for the planet Uranus features the capital letter H in his honor.
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Editor's Note: This article was updated on Nov. 5, 2018 to reflect a correction. The original article stated that Herschel died at the age of 84.