The 18th century, often referred to as the Age of Enlightenment, saw a steady increase in the study of the sciences. The abstract theorising of the Greek philosophers and the hit-and-miss approach of the medieval alchemists gave way to the sound scientific methods of experimental science as founded by Galileo and Newton in the previous two centuries.
Basically this involved the testing of theories by experiment or observation; thereby establishing whether or not the theory was correct. Astronomy in the 18th century, although it followed the rising tide of experimental and observational science, was also seen as important for the practical science of Navigation. Towards the end of the century several events and influences brought astronomy to prominence in the public eye.
These were:
- The importance of Astronomy for navigation which was necessary to facilitate trade with distant countries
- The success of Newton’s theory in predicting the movements of the planets and comets in the solar system
- Captain Cooke’s voyages of discovery and the Transit of Venus of 1769
- The discovery of Uranus by Herschel
Trade and Navigation
During the 17th and 18th centuries, trade with the Empire, particularly with the new world and India, was becoming increasingly important to Great Britain. With only primitive navigational methods at their disposal many ships were lost on the high seas and it soon became evident to the maritime authorities that improvements in the techniques of navigation were required. This lead directly to the setting up of the Royal Greenwich Observatory in 1675 which was charged with the duty of improving the accuracy of the positions of stars which could be used by mariners for determining their position at sea.
Understanding the motions of the planets
In the 17th century the great mathematician, Sir Isaac Newton, had proclaimed The Universal Law of Gravitation, which postulated that the same force that pulled the falling apple to the ground also held the moon in its orbit around the Earth and the planets in their orbits around the Sun. To accurately test Newton’s theory, precise measurements of the planets were required, these were to be provided by the new observatories.
The Transit of Venus and the Voyages of Captain Cook
As knowledge of the motions of the planets improved it became possible to make more precise predictions for the future. In 1769 it was predicted that the planet Venus would transit across the face of the sun as viewed from the Earth. It was realised that this rare event would provide a unique opportunity to determine the basic unit of the solar system, the distance from the earth to the sun, (called the Astronomical Unit) provided it could be observed from several stations around the world.
The Royal Society commissioned Captain Cooke to voyage to the Pacific to observe this event from the South Seas and to this end he carried with him an astronomer. It was during this voyage that Cooke annexed Australia.
Observations of the transit were also made by King George III from his new observatory at Kew, built specially for the purpose. The telescope by Short used by George III for this historic observation was presented to Armagh Observatory by Queen Victoria. A clock, by Shelton of London, was used by George III to determine the exact time of the apparition.
The transit of Venus in 1769 was also observed from Ireland using special instruments brought from London for the purpose. They were carried out at Cavan, a townland near Strabane, by Charles Mason (of Mason-Dixon Line fame).
The discovery of Uranus by Sir William Herschel
Sir William Herschel, a musician from Germany who settled in England, was probably the greatest astronomer and telescope builder of the 18th century. His telescopes, which were the largest and most powerful of their day, gave him a distinct advantage over his contempories and enabled him to discover many new nebulae and clusters of stars.
Planets, unlike stars, have a visible disc in a large telescope and in 1781 Herschel discovered a new planet which he named Georgium Sidus after George III, his patron. This was the first planet to be discovered since the time of the ancient Greeks and, not surprisingly, its discovery had a profound effect on the public; no longer were the heavens seen to be immutable from ancient times – there were new discoveries to be made in the solar system and beyond. The new planet later came to be known as Uranus.
