Edmund Halley: Comet Explorer and Stellar Cartographer

Edmund Halley
Edmund Halley. Public Domain

Meet the Man Behind the Comet

Ever hear of Halley's Comet? It has been known to humans for centuries, but one man dared figured out its orbit.  That man was Edmund Halley. He is famous the world over for the work he did to identify Comet Halley from orbital measurements. For his labors, his name was attached to this famous comet.

So, who was Edmund Halley? 

Edmund Halley's official birth date is November 8, 1656. At the age of 17, he entered Queen's College Oxford, already an expert astronomer. He carried with him a wonderful collection of astronomical instruments purchased for him by his father.

He worked for John Flamsteed, the Astronomer Royal and was so useful that when Flamsteed published his findings in Philosophical Transactions of the Royal Society in 1675, he mentioned his protegé by name. On August 21, 1676, Halley observed an occultation of Mars by the Moon and published his findings. An occultation occurs when one body passes between us and the more distant object. It is said to "occult" the other object.

Halley put his Oxford career on hold to go "on travel" and map the southern skies. He cataloged 341 southern stars and discovered a star cluster in the constellation Centaurus. He also made the first complete observation of a transit of Mercury. A transit occurs when Mercury passes or "transits" across the face of the Sun.These are rare events and give astronomers a chance to observe the size of the planet and any atmosphere it may have. 

Halley Makes a Name for Himself

Halley returned to England in 1678 and published his catalog of southern hemisphere stars. King Charles II decreed that the University of Oxford confer a degree on Halley, without his having to take exams. He was also elected a member of the Royal Society at 22, one of its youngest members. All these honors did not sit well with John Flamsteed. Despite his earlier liking of Halley, Flamsteed came to consider him an enemy.

Travels and Observations

During his travels, Halley observed a comet. He worked with Giovanni Cassini to determine its orbit.  that the inverse square law of attraction. He discussed Kepler's third law as a possible way of understanding that orbit with his colleagues Christopher Wren and Robert Hooke. He visited Isaac Newton and urged him to publish his Principia Mathematica, which discussed the same issues of planetary orbits.

In 1691, Halley applied for the Savilian Chair of Astronomy at Oxford, but Flamsteed blocked the appointment. So, Halley edited Philosophical Transactions, published the first actuarial tables, and made careful studies of comets. In 1695, when Newton accepted the position of Master of the Mint, he appointed Halley deputy controller of the mint at Chester.

Heading out to Sea and Into Academia

Halley accepted command of the ship Paramour, on a scientific expedition. He studied the variation between magnetic north and true north and published a map showing isolines, or points of equal value of deviation.

In 1704, he was finally appointed Savilian Professor of Geometry at Oxford, which upset Flamsteed. When Flamsteed died, Halley succeeded him as Astronomer Royal. Flamsteed’s widow was so angry she had her late husband’s instruments sold so Halley could not use them.

Discovering Comet Halley

Halley turned his attention to work he had started in 1682. Armed with Kepler’s Laws of Planetary Motion, and Newton’s theories of elliptical orbits, Halley recognized that the comets of 1456, 1531, 1607, and 1682 all followed similar paths. He then that these were all the same comet. After publishing his theory, Synopsis on Cometary Astronomy in 1705, it was simply a matter of waiting for the next return to prove his theory.

Edmund Halley died January 14, 1742, in Greenwich, England. He did not survive to see the return of his comet on Christmas day in 1758.