Halley, Edmond (1656-1743)

English astronomer

The son of a wealthy merchant, Edmond Halley was attracted to astronomy after seeing two comets as a child. By the age of eighteen, he had found errors in authoritative tables on the positions of Jupiter and Saturn and by nineteen, had published a paper on the laws of Johannes Kepler. In 1676, Halley left England for St. Helena, an island west of Africa, to map the southern constellations, a task never before undertaken. Although the climate of St. Helena proved less than ideal for Halley's purposes, he was able to catalogue 341 stars before returning to England. His pioneering work on the island assured his place in England's scientific community, and Halley was awarded a master's degree from Oxford as well as election to the Royal Society.

In 1684 Halley entered into a conversation with biologist Robert Hooke and architect Christopher Wren (1632–1723) that concerned the force that drove the movement of the planets. Unable to reach a satisfactory conclusion, Halley turned to his friend Isaac Newton. Discovering that Newton had already answered the question using his law of gravity, Halley convinced his reticent friend to publish his findings. Using funds bequeathed to him by his father, Halley financed the publication of Mathematical Principles of Natural Philosophy, now considered one of the classic texts of modern scientific thought.

At the age of 39 Halley turned his attention to comets, which, as they streaked unexpectedly through the sky, appeared ungoverned by Newton's law. Halley, however, believed that gravity did indeed dictate their path and that the rarity of their appearances was due to the vast length of their orbit, which was elliptical. With the help of Newton, Halley compared the paths of past comets that had appeared in 1531, 1607, and 1682. From this data he was able to determine that these seemingly separate comets were indeed the same comet and accurately predicted its reappearance in 1758. In 1705, Halley published his findings in A Synopsis of the Astronomy of Comets. Eventually, the comet that he predicted was named for him.

In addition to his findings concerning comets, Halley undertook a lengthy study of solar eclipses and discovered that the so-called fixed stars actually moved with respect to each other. He also wrote in favor of the theory that the universe is limitless and has no center. Halley's scientific interests, however, extended beyond astronomy. He played a major role in transforming the Royal Society from a social club into a well-respected clearing-house for scientific ideas. He devised the first weather map and calculated the amount of salt deposited by rivers into seawater over millions of years which allowed him to draw conclusions about the age of Earth. He also invented, developed, and tested one of the first practical diving bells. He served as chief science advisor to Peter the Great when the Russian czar came to England in an attempt to integrate Western advances into his country's society. From 1698 to 1700, Halley commanded the Paramour, a Royal Navy ship, for a scientific expedition which studied the effects of the Earth's magnetic field on magnetic needle compasses. He became Astronomer Royal in 1720, and continued to make astronomical observations and attend scientific meetings until shortly before his death in Greenwich at the age of 86.