Herschel-King’s Astronomer

Portrait of Sir William HerschelIn this article we learn how William Herschel became a famous astronomer and we summarize some of his later discoveries.

In 1781 Herschel was employed as a professional musician in Bath, Somerset, England. His successful musical career financed his hobby as amateur astronomer.

In the evening of Tuesday 13th March 1781 Herschel was in the back garden of his house in New King Street, Bath scanning the skies with his homemade seven foot reflector telescope.He started following a disk like object which was moving across the sky through the constellation of Gemini.

As he tracked this mysterious object he realized that its size was increasing all the time, indicating that the object must be orbiting the sun. It could not have been a comet since it did not have a distinctive comet ‘tail’.

Comet Ison orbiting Mercury

The sharp,round shape of the mystery object and the lack of a tail pointed to the discovery of only one thing ….. a new planet orbiting the sun!

Uranus

Uranus seen from Jodrell Bank Telescope in Manchester, England 

Herschel told the ‘Astronomer Royal’ Nevil Maskelyne about this exciting discovery. At first Maskelyne was sceptical  of Herschel’s claim to have discovered a new planet. After all, it was none other than Herschel himself who had previously claimed that ‘lunarians’ lived in settlements on the moon.

Why should Maskelyne believe Herschel now? Was this just another of his crazy theories?

So Maskelyne had no reason to accept Herschel as a reliable astronomer. Maskelyne faced being discredited and ridiculed if he were to support Herschel’s claim which later turned out to be wrong.

 Maskelyne painted by Gerald van de Puyl in 1785

Nevil Maskelyne

On the other hand, to reject what could be the greatest astronomical find of the 18th century would have been even more damaging. To ignore this new find would have allowed those great rivals the French astronomers to claim the discovery for France and give it a French name.

So Maskelyne did what every good scientist should do in the circumstances; he made his own observations and reached his own conclusions.

On 6th April 1781 Maskelyne felt sufficiently confident that a new planet did actually exist; he now informed Sir Joseph Banks, president of the Royal Society.

Portrait of Joseph Banks by William Daniel

Sir Joseph Banks

Maskelyne told Sir Joseph that the ‘musician of Bath’ had made a discovery which had ‘much merit’. Maskelyne further explained that, ‘Mr Herschel is undoubtedly the most lucky of astronomers in looking accidentally at the fixed stars with a seven foot reflecting telescope….’

uranus and its rings© Don Dixon at Cosmographica.com 

The belief that the discovery of this new planet had been somehow ‘accidental’ was a viewpoint that continued to be held for some months.

In an effort to refute this claim Herschel replied to Sir Joseph in a letter dated the 19th November,’the new star (ie planet) could not have been found out even with the best telescopes had I not undertaken to examine every star in the heavens … to the amount of at least eight to ten thousand’…. The discovery cannot be said to be owing to chance only it being almost impossible that such a star should escape my notice’.

Other sceptics from the Royal Society maintained that Herschel had greatly exaggerated his claim to have discovered a new planet using a telescope that magnifies objects 6450 timeOne of their number had calculated that a star so highly magnified would be difficult to see since it would pass through the viewing field of his telescope exceptionally fast  and disappear in ‘less than a second’.

Herschel’s response was that it took all of three seconds and he could move his telescope around to follow stars perfectly well.

Engraving after 'Men of Science Living in 1807-8 by George Zobel, and William Walker engraving from1862

Distinguished men of science meet in 1807

To settle the controversy once and for all Maskelyne himself tested Herschel’s seven foot telescope at the Greenwich Royal Observatory in London.

Maskelyne was stunned by the superior quality and light collecting power of Herschel’s telescope, immediately recognising it to be far more powerful than any other telescope in existence at the time.

Royal Observatory Greenwich, London in 1824

Royal Observatory in Greenwich, London, early 19th century

Naming the new planet

Herschel named his new planet ‘Georgium Sidus’ or ‘George’s Star’. He conferred this name in honor of George the third, the king of England and fellow German from the City of Hanover.

Other European astronomers preferred the name Uranus, a more neutral name which had no associations with Britain. In ancient Greek mythology Uranus was the god of the sky and first ruler of the universe.

The ‘name ‘Uranus’ was not universally adopted by all until the middle of the 19th century.

Sir Joseph Banks introduced Herschel to King George at Windsor Castle (20 miles west of London) in May 1782. The meeting between the two Germans, both speaking in English, was a great success. The king appointed Herschel as his personal astronomer at Windsor on a salary of £200 a year.

King George III looking resplendent in coronation robes

King George III

As the king’s personal astronomer Herschel needed to be close to Windsor Castle.

The Town Gate looking westwards down Castle Hill, Windsor, c.1765 painted by Paul and Thomas Sandby

 Windsor was King George III’s occasional country retreat…

North Terrace Windsor Castle in 1790 painted in watercolour by Paul and Thomas Sandby

 …and only 20 miles from the king’s main London residence at Buckingham Palace.

Buckingham Palace engraved by J.Woods in 1837 showing people and soldiers

 On the 31st July 1782 Herschel moved to a house in the village of Datchet just outside Windsor so he could be close to the king.

Map of South Britain in18th century showing Datchet and Windsor

Almost immediately the king commanded Herschel to bring his seven foot telescope to Windsor Castle where it was reassembled for the king’s family and friends to view the night sky.

Herschel's seven foot reflector telescope

The three teenage royal princesses Charlotte, Augusta and Elizabeth took a particular interest.

Charlotte, Augusta and Elizabeth daughters of King George the third

It was not long before Herschel moved to a large rambling house in Slough, also near Windsor. His new house, called ‘The Grove’, had a larger garden suitable for erecting more powerful telescopes. It also had stables which Herschel converted into workshops for making his precious telescopes.

Herschel got to work and built a 20 foot reflector telescope…

Herschel's 20 ft telescope in the garden of Herschel's house in Datchet

… followed soon afterwards in 1785 by a monstrous 40 foot reflector telescope!

Herschel's 40 foot telescope

The great 40 foot telescope

However building the 40 foot telescope was beset with problems. Herschel wasted £500 on casting a new mirror that proved to be faulty. He seriously underestimated the construction costs of casting a large mirror, especially the cost of employing workmen to laboriously polish the new mirrors.

The Morning Walk by Thomas Gainsborough

High society attended the garden party

The large mirror also proved incredibly difficult to insert and remove from the tube. On one occasion Herschel was nearly crushed as he helped remove the one ton mirror from the tube when it needed polishing.

Herschel’s whole project was threatened by bankrupcy. He urgently needed to secure additional funding.

On 17th August 1787 Herschel organized a garden party at his house in Slough to show the king his new 40 foot telescope.

The party was attended by King George III,Queen Charlotte, the royal household, many lords and ladies not forgetting distinguished foreign visitors.

The garden party proved a great success. The king now granted Herschel an additional £2000 to finish his telescope project and secure its future.

However the forty foot telescope continued to be plagued by problems and in the five years between 1788 and 1793 Herschel only managed seventeen nights of ideal observations.

The telescope was difficult to maneuver and did not perform well under adverse weather conditions including frost, conditions of high humidity and changes in air temperature. It was the 20 foot telescope that proved more reliable and which Herschel used for most of his stat gazing.

From the garden of his house in Slough Herschel made some amazing discoveries.

The discovery of Mimas and Enceladus

Herschel discovered two moons of Saturn, Mimas and Enceladus, in 1849.

Saturn and its moons

Mimas is mainly composed of ice and rock. It has a surface area the size of Spain. Its most distinctive feature is a giant impact crater named ‘Herschel’ 130 kilometers (81 miles) in diameter. Its walls are 5 kilometers (3.1 miles) high and its central mountain rises 6 kilometers (3.7 miles) above the crater floor.

Mimas

The moon Enceladus has a series of deep fissures running along its length.

Enceladus showing fractures at south pole

These fissures are colored blue as a result of ice freezing onto the fissure walls. Ice volcanoes (or’cyro volcanoes’) located inside the fissures shoot jets of water, ice particles, dust and small stones into space. Some material falls back onto the moonscape while the remainder escapes into space.

Saturn's moon Enceladus venting

It is all this material spewing out from Encladus that has created one of Saturn’s rings, the so called ‘E Ring.’

Enceladus and saturn's E ring

The ‘cyro volcanoes’ found inside the fissures point to the existence of a sub surface ocean of liquid water- a  exciting possibility that may indicate the existence of some form of life existing in one of Saturn’s moons!

Herschel’s discovery of Titania and Oberon

On 11th January 1787  Herschel discovered two moons of Uranus- Titania and Oberon.

moons of uranus

Titania, (not to be confused with the moon ‘Titan’ orbiting Saturn) is the largest of all Uranus’s moons with a diameter of 1,578 kilometers (981 miles).

Titania probably has a rocky core, an icy mantle and a layer of liquid water located at the boundary between the core and mantle.  The surface of Titania is covered with numerous impact craters and deep canyons. Titania’s surface is also covered with frozen water ice and frozen carbon dioxide.

Titania, moon of Uranus showing impact craters and canyons

Oberon is the outermost and second largest of Uranus’s moons. Its orbit lies partially outside Uranus’s magnetic field  (or ‘magnetosphere’). As a result it receives little protection from lethal doses of solar radiation which constantly bombards its surface.

Its geology is similar to Titania’s; it has a rocky core, an ice mantle and numerous impact craters resulting from collisions with asteroids and comets.

Moon Oberon showing impact craters and icy surface

Only 40% of Oberon’s surface has ever been mapped

Herschel’s discoveries about Mars

Herschel measured the axial tilt of Mars….

axial tilt of Earth and Mars compared

……and discovered that the martian ice caps frequently change size depending on the season.

mars northern ice cap changes with the seasons

Herschel invents the term ‘asteroid’

In 1802 William Herschel invented the term ‘asteroid’ from the words ‘star’ and  ‘shape’ in ancient Greek. Today we use the term ‘asteroid’ to describe minor planets in our solar system. Most of these minor planets, which vary considerably in size, orbit the sun between Mars and Jupiter in the so called ‘Asteroid Belt’.

Asteroid belt beteen Mars and Jupiter

One of the largest asteroids in the Solar System is Vesta located in the inner Asteroid Belt. It has a diameter of 525 kilometers (326 miles) and was discovered in 1807 by another German astronomer Heinrich Olbers.

Vesta asteroid

William Herschel discovers infrared radiation

On 11 February 1800 Herschel was looking for ways to observe the sun through a telescope without damaging his eyes. At the time he was researching sunspots and needed to look directly at the sun. As a way of protecting his eyes he tested out different colored filters which he designed to attach over the eyepiece.

image of our sun showing sunspots One of the filters he tested was colored red. When he looked at the sun through his telescope using a red filter he noticed his eye warming up more than was usual.

Deciding to investigate this curious phenomenon further he put his telescope aside and conducted an experiment with a prism.

He passed visible sunlight through a prism and held a thermometer inside the rainbow of colors.

,visible sunlight passes through a prism producing colours of the rainbow

Using a thermometer he recorded the temperature inside the rainbow of colors (the visible spectrum of light) Next he held the thermometer just beyond the visble red spectrum of light. When he did this he noticed that the temperature actually increased.

Herschel had discovered infrared radiation, that invisible spectrum of light that allows us to feel the warmth of the sun on our skin. (for an explanation of infrared radiation read Earth as a Magnet )

William Herschel- a musician of many talents

William Herschel was a true polymath. During his lifetime he not only composed 24 symphonies , 14 concertos and 6 sonatas….

Vienna Mozart orchestra performing in period costume

…but also used a microscope to establish that corals are animals and not plants, as most scientists at the time believed.

Coral reef showing different types of corals

Corals do not make their own food, as plants do. Corals use their tiny, tentacle-like arms to capture their food from the water which they then feed into their mouths.

Science Fair Projects

  • Research places named after William Herschel including Herschel’s Garnet star, the ‘Herschel’ crater on the moon, the ‘Herschel’ impact crater on Mars and the ‘Herschel 2000’ asteroid.
  • Write about the discoveries that Herschel made which furthered our understanding of astronomy.
  • Investigate the life and times of William Herschel.
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