Edmund Halley

Born November 8th, 1656 in Haggerston, England to a prosperous family, young Edmund Halley received a private education before enrolling in St. Paul's school. While in school, Edmund excelled in mathematics and astronomy. At the young age of 17, he enrolled at The Queen's College, Oxford to study under the Astronomer Royal of the time John Flamsteed

By 1676, Halley had dropped out of university to begin making his own contributions to the field of astronomy. After publishing his star chart of the southern oceans in 1678, he was granted a Master of Arts from Oxford by decree of King Charles II. Anchoring his position as a great astronomer, Halley was also elected fellow of the Royal Society as one of the youngest members.

At the young age of 22, he sailed to St. Helena where he discovered a star cluster in Centaurus and mapped the stars of the southern hemisphere, allowing sailors to navigate the world's oceans. Halley devised a clever way to calculate the distance from the Earth to the Sun. By carefully timing how long it took Venus to cross the Sun's disk, he was able to give a real distance to the astronomical unit; about 93 million miles. He used this newfound information to accurately calculate the size of the solar system for the first time.

Pouring over ancient Greek recordings of stars, Halley compared their observations to what he saw in the night sky some 1800 years later. He discovered that the stars the Greeks had cataloged were not in the same position as the stars he observed, but had moved. Halley concluded that the stars are not fixed in one position as once thought, their motion only apparent to the observer after many centuries.

Continuing his pioneering work in observational astronomy, Halley published in 1705 A Synopsis of the Astronomy of Comets, in which he described the parabolic orbits of 24 comets that had been observed from 1337 to 1698. He showed that the three historic comets of 1531, 1607, and 1682 were so similar in characteristics that they must have been successive returns of the same visitant—now known as Halley’s Comet—and accurately predicted its return in 1758.

His Early Career and Travels

In 1675, Halley became the assistant for John Flamsteed who was first Astronomer Royal at Greenwich Observatory. One of Halley’s many tasks was to assign numbers to stars using Flamsteed’s number system for identification and cataloguing purposes. A year later, he travelled to the volcanic tropical island Saint Helena, in the South Atlantic Ocean. He brought with him a large sextant and some telescopic sights so he could set up an observatory and study and catalogue the stars in the Southern Hemisphere. It was during his stay in St. Helena that he carefully observed the transit of Mercury across the sky. He realized that Venus, moving in the same way, could then be used to calculate the size of the Solar System.

Halley returned to England in 1678 and a year later he went to Danzig at the request of the Royal Society to help resolve a dispute between Robert Hooke and Johannes Hevelius. As Hevelius did not utilize a telescope in his observations, Robert Hooke questioned his findings. Halley stayed with Hevelius to observe his findings and verify his conclusions

That same year in 1679, Halley published “Catalogue Stellarum Australium”, a catalogue of the Southern Hemisphere stars which he observed while in St. Helena. His publication was so extensive that it included 341 stars that could be viewed only in the Southern Hemisphere. Flamsteed gave him the title “The Southern Tycho” in reference to the well-known sixteenth century astronomer, Tycho Brahe. Halley also attained his Master’s Degree from Oxford and was elected as a Royal Society Fellow aged 22.

Halley conducted many lunar observations which took up most of his time. Aside from his lunar studies, he also became interested with problems relating to gravity. One issue in particular that concerned him was finding a proof for the laws of planetary motion. In 1684, he travelled to Cambridge to talk the issue over with Sir Isaac Newton, only to find out that Newton had already managed to solve the problem, stating that the planets’ orbits would be elliptical. Halley naturally wanted to see the calculations Newton used but Newton wasn’t able to locate them. Newton then wrote a short treatise entitled “On the Motion of Bodies in an Orbit” in 1684 which explained his calculations. This work was later expanded on by Newton, becoming the famous work “Philosophiæ Naturalis Principia Mathematica” in 1687 which Halley helped to publish.

Later Life and Comet Predictions

In 1698, he was given permission to take command of the sailing ship Paramour and travel to the South Atlantic Ocean to find out more about the laws that govern the variation of the compass. The first expedition was cut short due to unrest among the crew and a second expedition began in 1699. His magnetic charts of Atlantic Ocean and parts of the Pacific Ocean were published in “General Chart of the Variation of the Compass” in 1701.

In 1704, Halley finally became Savilian Professor of Geometry at the University of Oxford, after missing out on this prestigious appointment earlier in his career. He published “Synopsis Astronomia Cometicae” (A Synopsis of the Astronomy of Comets) in 1705. This work detailed the parabolic orbits of 24 comets that had been observed from 1337 to 1698. It also stated that the comet sightings of 1531, 1607, and 1682 were of the same comet, which orbits the sun every 75-76 years and he correctly predicted it would return in 1758. When the comet did return it became known as Halley’s Comet.

He devised a method of observing the transit of Venus across the sun which would next be observed in 1761 and 1769. These observations would then be used to make an accurate calculation of the distance from the Earth from the sun.

Halley became Astronomer Royal at Greenwich Observatory, succeeding John Flamsteed in 1720.

His death

He died on January 14, 1742 aged 86 and sadly, did not live to see the return of the comet that was named in his honor. Halley’s Comet will next appear in the night sky in the year 2062.