Edmond Halley has arguably one of the best-known scientific legacies of any figure of the Scientific Revolution: every 76 years, all one has to do is look up into the night sky and you'll see the comet that bears his name. But while just about every school kid learns about Halley's Comet, and many will live to see it in their lifetimes, there is much more to the man than his famous comet.
A renowned astronomer, Halley was making major scientific contributions before he even finished his undergraduate education, including producing Europe's first star catalog of the skies of the Southern Hemisphere and was the first to record the complete transit of Mercury in 1677.
As a colleague and friend of Isaac Newton – as much as one could be a friend to the notoriously aloof and cantankerous genius – Halley was instrumental in publishing Newton's findings on the laws of motion and gravitation, which would set the course of physics for the next two and a half centuries.
Halley was a true man of science, who sought to advance the cause of human knowledge, sometimes at his own expense, and even if he himself would never live long enough to see the rewards of his endeavors despite a long and fruitful life.
Early life and career
Edmond Halley – traditionally pronounced to rhyme with "alley" – was born on November 8, 1656, in Haggerston, England (part of today's London), to a well-to-do merchant family.
His father was a London soapmaker whose wealth enabled him to indulge his son's scientific curiosity – so much so that when Halley finally went off to Queens College, Oxford, in 1673, the young lad brought some seriously hardcore astronomy equipment with him.
At Oxford, the young astronomer became the protégée of John Flamsteed, England's first Astronomer Royal (Halley would later become England's second). With Flamsteed's guidance, Halley published his first papers in 1676 while still an undergraduate.
The formal academic life couldn't hold a candle to "fieldwork", and so inspired by Flamsteed's project to create a formal star catalog of the northern hemisphere, Halley proposed that he would do the same for the southern hemisphere.
Like many undergraduates of his day, Halley left school without bothering to take a degree, received funding from no one less than King Charles II himself, and sailed to St. Helena Island off the coast of West Africa. There, he spent an entire year there cataloging nearly 350 stars and their positions in the southern sky and even used some known, visible northern stars for reference points.
While he was there, Halley discovered a star cluster in Centaurus and also became the first person to ever record the entire transit of Mercury, an experience that left an indelible mark on him, and later, the entire world.
Early work with comets
After his return to England, Edmond Halley published his star catalog in 1678 and it cemented his reputation as a serious astronomer in an era full of serious astronomers. King Charles II decreed that Halley be granted a Master of Arts degree from Oxford and he was invited to join The Royal Society at just 22, making him one of the youngest ever granted that honor.
Rather than take up an academic post, Halley traveled – as all good 20-somethings are supposed to do – making scientific observations along the way. While visiting with Giovanni Cassini in France, Halley observed a commet and attempted to plot the course of its orbit, and failed.
While scientists like Tycho Brahe, Galileo Galilei, and Johannes Kepler had turned their telescopes to the heavens and made major strides in our knowledge of the planets, no one really knew what comets were or how they worked, so Halley's failure wasn't entirely his doing. When the shoulders of the giants you are standing on are facing the wrong way, you're going to get it wrong too.
The problem was that while large celestial bodies like planets were seen to orbit the sun, and moons were seen orbiting planets, the same couldn't be said of comets. They did not seem to have any period that anyone could measure and it was widely believed that they traveled in a straight line or followed parabolic paths that flung them back out into deep space, never to return.
After his frustration with the Great Comet of 1680, Halley swore to do a better job next time. He wouldn't have to wait long to try again, as it turned out.
Soon after returning to England, Halley returned to conducting observations through the telescope at his home. In 1682, another comet fortuitously made an appearance, and Halley made a far more diligent study of it than he did with the Great Comet of 1680. It would be the start of his most important legacy, though it would be many years before he would truly appreciate its significance.
Learning to sail (and learning to swear)
En route to making his mark on history, Edmond Halley took his time and traveled the world, performing experiments at sea while acting as the commander of a ship – though he had no prior experience actually working on a vessel – and appears to have taken to it quite well.
He would go on to publish the first-known meteorological chart in 1686, plotting out the tradewinds of the Atlantic, South Pacific, and Indian Oceans.
He also reportedly has taken to drinking and getting rather loose with his language, something that would later come back to haunt him in England when he went looking for more steady work as an academic.
When he was finally given a post in 1704 as the Savilian professor of geometry at Oxford, Flamsteed, his old mentor-turned-critic, complained that Halley "now talks, swears and drinks brandy like a sea captain."
Isaac Newton and Edmond Halley
It was shortly after this appointment that Halley would make his mark on history for good, though we cannot talk of Halley's comet without involving the mercurial Isaac Newton, whose work would become intertwined with Halley's own.
In 1682, around the time Halley was observing the most famous comet in the world, he was also deeply involved in the study of Johannes Kepler's work on planetary motion, namely that of elliptical orbits of planets around the Sun.
Kepler had only observed this phenomenon since he could not explain the mathematical basis of orbits. Halley wondered if comets might also have such orbits, but was unable to wrap his head around the physics of such a thing. Fortunately for Halley, he knew someone who could.
In 1684, Halley was discussing the problem with noted physicist Robert Hooke and the architect Christopher Wren in a London coffeehouse. Stymied, Halley paid a visit to Isaac Newton to discuss the matter with him. It was at this meeting that Newton revealed that he had already worked out a solution a few years before for another comet, but had set the matter aside.
Halley wanted to see the calculations, though Newton no longer had them, so he rewrote them and sent them to Halley in November 1684 in manuscript form.
Halley, recognizing the profound significance of this discovery more than even Newton himself, pushed Newton to expand his studies and publish his work, going so far as to personally finance its printing, since the Royal Society currently didn't have the means to do so. Halley wasn't much better off financially, but he made the investment anyway, much to the world's benefit.
So, Philosophiae Naturalis Principia Mathematica ("Mathematical Principles of Natural Philosophy"), Isaac Newton's most important work, and the cornerstone of physics and classical mechanics for more than 200 years, was largely made possible by Halley's insistence and aid, elevating another's greatness at his own personal expense for the sake of scientific discovery.
Not satisfied to simply publish Newton's work, though, Halley would soon become instrumental in proving, in real terms, the veracity of Newton's laws in the most spectacular way possible.
On the comet that bears his name
It would be many years before Halley returned to the study of comets, but he did eventually return to it starting around 1695. He had become convinced that the comet of 1680 did in fact have an elliptical orbit and that the same comet returned many times throughout history.
Exploring the historical record for comet sightings, Halley calculated that the comet he had studied in 1682 was the same comet identified in 1305, 1380, 1456, 1531, and 1607. Then, in 1705, he rolled the dice and made a bold prediction. Halley published "A Synopsis of the Astronomy of Comets" in 1705, in which he wrote:
"Many considerations incline me to believe the Comet of 1531 observed by Apianus to have been the same as that described by Kepler and Longomontanus in 1607," Halley wrote, "and which I again observed when it returned in 1682. All the elements agree. Whence I would venture confidently to predict its return, namely in the year 1758."
He would be long dead by then, he knew, but using Newton's laws of motion, he was able to calculate the orbit of the comet with incredible precision and staked his reputation on his – and by extension, Newton's – figures.
When the comet appeared as predicted on December 25, 1758, Halley's Comet, as it came to be known, proved Newton correct and made Halley a household name, even to this day.
The transit of Venus and the Solar Parallax
The periodicity of Halley's comet wasn't the only important scientific prediction that Halley made in his later career.
By the 18th century, astronomers had been able to calculate the relative distances between all of the major bodies in the known solar system, but they had no way of knowing what these distances were in absolute terms. The most important of all these distances was the astronomical unit (AU), the distance between the Earth and the Sun.
The problem was that no one had any idea how big the sun actually was. If the sun were the size of the moon, Earth could be orbiting at a distance of just 238,900 miles, while Jupiter, Mars, Venus, and Mercury could be much smaller and much nearer, relatively speaking.
Simply put, no one knew how large the solar system was, but we did know how large the Earth was. By observing a transit of a planet in front of the Sun from several points on the Earth's surface and recording the critical ingress and egress times of the planet's silhouette, finding the distance between the Earth and the Sun was simply a matter of trigonometry, using something known as the solar parallax.
As a young man, Halley's observation of the Transit of Mercury in 1677 was made in the hope of calculating the solar parallax, but only one other record of the Transit of Mercury has been made, which wasn't sufficient to identify an accurate parallax.
Since transits are exceptionally rare events, the next chance anyone would have to use a planetary transit to calculate the solar parallax would be the next Transits of Venus, set to occur in 1761 and in 1769. The world wouldn't get another chance until 1874.
In 1691, and later in 1716, Halley published a public call for international cooperation between nations to send out scientific expeditions around the world to record the Transit of Venus in order to calculate the astronomical unit and reveal the scale of the solar system for the first time.
Though he wouldn't live to see it himself, the international community did indeed take up his call, and scientists from Britain, France, Russia, the United States, Canada, and others recorded the event in 1769, determining a figure for the solar parallax that gave a very close approximation of the astronomical unit that was only about 3% off its actual value.
Death and legacy
In 1720, Halley succeeded Flamsteed as Astronomer Royal. He died on January 14, 1742, in Greenwich, England.
Edmond Halley never got to see his two most notable contributions to our scientific understanding of the universe play out. As many have noted before, his work had the unfortunate handicap of being carried out in the shadow of Isaac Newton, one of the greatest scientific minds humanity ever produced. But even though Halley never got to find out how big the universe is, much less our own small corner of it, we owe that knowledge in no small part to his work – and what better way of leaving your mark on the world than having one of the greatest once-in-a-lifetime spectacles humans have ever seen named in your honor?