Halley's comet

It's ironic that one of the greats of British science is commonly remembered for something he didn't do. Despite his numerous accomplishments in many fields, Edmond Halley never discovered a comet.

Halley was born in Haggerston (now part of London) on November 8, 1656 and he lived in the London area for the rest of his life. His father was a well-to-do merchant who was able to send his son to the distinguished St Paul's School, then to Oxford, and after that provide him with an allowance so that he could continue his scientific work.

An outstanding student at St. Paul's School, Halley was 17 when went to Queen's College, Oxford. As an undergraduate he worked with the Astronomer Royal John Flamsteed during the vacation.

These days many 19-year-olds take a gap year. Halley however didn't so much take a break as simply abandon his degree course to spend two years cataloging the stars of the southern skies – a complement to the star catalog Flamsteed was making for the northern skies. It says a lot about Halley that he not only persuaded his father to finance the project, but also obtained influential support for it, including that of the king.

His destination was the island of St Helena in the South Atlantic, the southernmost outpost of the British Empire at that time. Halley's observations led to the Catalogus Stellarum Australium (Catalog of Southern Stars), which he presented to the Royal Society. The Society responded by electing him to membership – he was 22 then, and was compared to Tycho, the great Danish observer.

Halley made a planisphere of the southern skies and dedicated it to King Charles II. (A planisphere is a star map that can be adjusted for date and time.) In recognition of Halley's work, the king ordered Oxford to award Halley a degree, an offer they couldn't refuse.

In 1682 both Halley and his father got married. The younger Halley married Mary Took. They settled in Islington (now part of north London) and had three children. The widowed elder Halley remarried, but the marriage wasn't a success.

A family tragedy occurred in 1684 when the elder Halley disappeared and was found dead, presumably murdered, several weeks later. His son had to devote a lot of time to getting his father's estate sorted out.

Scientifically, one problem that interested Halley and his intellectual circle was that of orbits and gravitational attraction, but they couldn't find a solution. Halley went to discuss it with his friend Isaac Newton, only to find that Newton had already solved it, but wasn't interested in publishing. Halley not only persuaded him to publish, but actually corrected the proofs and paid for publication. (He did get his money back on the sales.) Newton's Philosophiae Naturalis Principia Mathematica - commonly known as the Principia - is one of the most important works in the history of science.

The name Halley is widely known because of the comet called after him. Halley saw the comet from his home in Islington soon after his marriage, but it was some thirteen years later that he began to work seriously on cometary orbits, using Newton's theories. He was sure the comet was the same as some that had been seen before. Calculating that it came back every 75.5 years, he predicted its return in December 1758.

Halley was many years dead when the comet was spotted on Christmas Day 1758. It caused a stir and became known as Halley's Comet. Edmond Halley was the first to identify a periodic comet and predict its return.

Another idea that came to fruition after his death was that of using a transit of Venus and some geometry to determine the distance from the Earth to the Sun. (In a transit we see the planet crossing the face of the Sun.) On St Helena, Halley had seen a transit of Mercury, but the next transit of Venus didn't occur until nearly twenty years after his death. Nevertheless expeditions were sent to collect the necessary data from the 1761 transit.

Although Halley had independent means, he also had a family, so was ready to consider paid jobs. He worked for the Royal Society and later the Royal Mint, but his first application for a professorship at Oxford failed. It seems that some thought his religious views were somewhat unorthodox. Years later he did get the appointment as Savilian Professor of Geometry. He also succeeded Flamsteed as Astronomer Royal. By then he was nearly 65 – retirement age for many today – but he did the job for twenty years until his death on January 14, 1742.

Halley didn't just study astronomy. He published papers in pure mathematics, meteorology, and almost as many in geophysics as in astronomy. Also closely involved in improving cartography and navigation, he wasn't one just to sit around theorizing about them. Uniquely, Halley was given command of a naval vessel by King William III in order to carry out his research.

In addition to his wide-ranging intellectual achievements, Halley was known for his sense of humor, adventurous spirit and his diplomacy. He could be a jolly drinking companion of the Czar of Russia, but also get along with the prickly Isaac Newton.

Halley's most enduring contribution to astronomy was his promotion of Isaac Newton's Principia, for a workable theory of gravity was key to modeling the cosmos. (There is a link below to "Gravity – Cosmic Glue" with more information.) It's true that Halley couldn't have done his work on comets without Newton's theory. Yet we need to realize that Halley's work, in turn, was an important verification of Newton's theory.

Reference:
Hide, R & Wolfendale, A (1993) "Edmond Halley – A Commemoration" Q.J.R. astr. Soc., 34, 135-149