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Today in science: Edmond Halley

He’s the astronomer for whom Halley’s Comet is named. It was the first comet ever predicted to return.

Comet Halley, photographed in 1986, via NASA.

Comet Halley, photographed in 1986, via NASA.

November 8, 1656. English astronomer and mathematician Edmond Halley was born near London, England, 360 years ago today. He was the first to calculate the orbit of a comet, today one of the most famous of all comets, named Comet Halley in his honor. He was also friends with Isaac Newton and contributed to Newton’s development of the theory of gravity, which helped establish our modern era of science, in part by removing all doubt that we live on a planet orbiting around a sun.

Read more: Comet Halley, parent of 2 meteor showers

Portrait of Edmond Halley circa 1687 by Thomas Murray via Wikimedia Commons.

Portrait of Edmond Halley circa 1687 by Thomas Murray via Wikimedia Commons.

The 17th century was a very exciting time to be a scientist in England. The scientific revolution gave birth to the Royal Society of London when Halley was only a child. Members of the Royal Society – physicians and natural philosophers who were some of the earliest adopters of the scientific method – met weekly. The first Astronomer Royal was John Flamsteed, who is remembered in part for the creation of the Royal Observatory at Greenwich, which still exists today.

After entering Queen’s College in Oxford in 1673, Halley was introduced to Flamsteed. Halley had the chance to visit him in his observatory on a few occasions during which Flamsteed encouraged him to pursue astronomy.

Royal Observatory at Greenwich via Wikimedia Commons.

Royal Observatory at Greenwich by Kjetil Bjørnsrud via Wikimedia Commons.

At that time, Flamsteed’s project was to assemble an accurate catalog of the northern stars with his telescope. Halley thought he would do the same, but with stars of the Southern Hemisphere.

His journey southward began in November 1676, even before he obtained his university degree. He sailed aboard a ship from the East India Company to the island of St. Helena, still one of the most remote islands in the world and the southernmost territory occupied by the British. His father and King Charles II financed the trip.

In spite of bad weather that made Halley’s work difficult, when he turned to sail back home in January 1678, he brought records of the longitude and latitude of 341 stars and many other observations including a transit of Mercury. Of the transit, he wrote:

This sight … is by far the noblest astronomy affords.

May 9, 2016, transit of Mercury from Vegastar Carpentier Photography in France.

May 9, 2016, transit of Mercury from Vegastar Carpentier Photography in France. Mercury is the small black dot on the left side the sun, in this image. See more photos of the 2016 Mercury transit.

Halley’s catalog of southern stars was published by the end of 1678, and – as the first work of its genre – it was a huge success. No one had ever attempted to determine the locations of southern stars with a telescope before. The catalog was Halley’s glorious debut as an astronomer. In the same year, he received his M.A from the University of Oxford and was elected a fellow of the Royal Society.

Halley visited Isaac Newton in Cambridge for the first time in 1684. A group of Royal Society members including physicist and biologist Robert Hooke, architect Christopher Wren and Isaac Newton were trying to crack the code of planetary motion. Halley was the youngest to join the trio in their mission to use mathematics to describe how – and why – the planets move around the sun. They were all competing against one another to find the solution first, which was very motivating. Their problem was to find a mechanical model that would keep the planet orbiting around the sun without it escaping the orbit or falling into the star.

Hooke and Halley determined that the solution to this problem would be a force that keeps a planet in orbit around a star and must decrease as the inverse square of its distance from the star, what we today know as the inverse-square law.

Hooke and Halley were on the right track, but they were not able to create a theoretical orbit that would match observations, in spite of a monetary prize to be given by Wren.

Halley visited Newton and explained the concept to him, also explaining that he couldn’t prove it. Newton, encouraged by Halley, developed Halley’s work into one of the most famous scientific works to this day, Mathematical Principles of Natural Philosophy, often referred to simply as Newton’s Principia.

Copy of the third edition of the Principia (1726) at the John Reynolds Library in Manchester, England via Wikimedia Commons.

Copy of the third edition of the Principia (1726) at the John Reynolds Library in Manchester, England via Wikimedia Commons.

The Royal Society decided that Halley should edit the Principia and finance its printing. Halley skillfully repressed a credit dispute between Hooke and Newton, edited the proofs, wrote the preface in Latin, praising the author of the book, and attended to its printing in 1687.

Halley is also known for his work in meteorology. He put his talent of giving meaning to great amounts of data to use by creating a map of the world in 1686.

The map showed the most important winds above the oceans. It is considered as the first meteorological chart to be published.

Edmund Halley's 1686 map of the world, which charts the directions of trade winds and monsoons and is considered the 1st meteorological map.

Edmond Halley’s 1686 map of the world, which charts the directions of trade winds and monsoons and is considered the 1st meteorological map, via princeton.edu.

Halley kept travelling and working on many other projects, such as attempting to link mortality and age in a population. This data was later used by actuaries for life insurance.

He became a professor of Geometry in Oxford in 1704. The following year, he published A Synopsis of the Astronomy of Comets. The book contains the parabolic orbits of 24 comets observed from 1337 to 1698.

It’s in this book that Halley remarks on three comets that appeared in 1531, 1607, and 1682. He noted they were so similar that they must be in fact one comet, which returns periodically every 76 years. It was an astounding notion at the time. He then predicted the comet to return in 1758, saying:

In the year 1456 … a Comet was seen passing Retrograde between the Earth and the sun… Hence I dare venture to foretell, that it will return again in the year 1758.

His observation was correct. This comet is now called Halley’s Comet, famous for centuries for being the first comet ever predicted to return.

In 1720, Halley succeeded Flamsteed and became the second Astronomer Royal at Greenwich.

Comet Halley's orbit via University of Rochester

Comet Halley’s orbit via University of Rochester.

Halley's Comet photographed in 1986 via NASA.

Halley’s Comet photographed in 1986 via NASA.

Bottom line: Astronomer Edmond Halley – for whom Halley’s Comet is named – was born on November 8, 1656.

Daniela Breitman

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