An Introduction to Halley’s Comet

Image Credit: NASA

Halley’s Comet, officially known as 1P/Halley, is a short-period comet visible from Earth every 75–76 years. It is the most famous known comet and is the only known short-period comet that is regularly visible to the naked eye from Earth and thus can be viewed twice in a human lifetime. The comet made its last appearance in 1986 and will next appear in mid-2061. 

Comet Halley was the first comet recognized as a periodic or short-period comet, with an orbit lasting 200 years or less. Its shape vaguely resembles that of a peanut shell, and its dimensions are about 9.3 by 5 miles (15 kilometres by 8 kilometres). It is one of the darkest or least reflective objects in the solar system, reflecting only 3% of the light that falls on it.  While it travels around the Sun, Halley leaves behind a trail of dust and ice particles that form the annual Orionid Meteor shower every October.

Origin:

Halley’s periodic returns have been subject to scientific investigation since the 16th century. Although it was around for centuries, it wasn’t until 1705 that Edmond Halley, an English astronomer and physicist, calculated its orbit and predicted its next appearance. He noted the three occurrences of the comet, used Isaac Newton’s recently developed Laws of Motion and some observational records and concluded that the comets which appeared in 1531, 1607, and 1682 were the same comet, and predicted that it would appear again in 1758. As foretold, the comet did reappear, but unfortunately, Edmond Halley wasn’t around to see its appearance. In 1759, Nicholas-Louis de Lacaille, a French astronomer, named the comet after Halley to honour him.

History of the Comet:

Some historians believe that the comet was sighted as early as 467 BCE by the ancient Greeks. A comet in ancient Greece, recorded between 468 and 466 BC with its timing, location, duration, and an associated meteor shower all suggest it was Halley.

The first official known sighting of this comet, according to historical records, occurred in the year 240 BC. The Chinese recorded this sighting in the Chinese chronicle ‘Records of the Grand Historian’ or ‘Shiji’, which describes a comet that appeared in the east and then moved north. 

In 1066, the comet was seen in England and was considered an omen. Later that year, King Harold II of England was overthrown and killed at the Battle of Hastings by William the Conqueror, who then claimed the throne.  The battle depicted on the Bayeux Tapestry chronicles those events and prominently displays the comet as a star. 

In 1456, on a return passage, Pope Calixtus III determined that the comet was an agent of the devil, attempted to excommunicate this natural phenomenon, and ordered special prayers for the city’s protection. His misguided attempt to frame it as a religious issue failed because the comet came back 76 years later. 

He wasn’t the only person of the time to misinterpret what the comet was. Around the same time, while Turkish forces laid siege to Belgrade, the comet was described as a fearsome celestial apparition “with a long tail like that of a dragon.”

Modern Observations:

The comet’s reappearance in 1986 sparked great interest in scientists around the world, who planned extensive plans to observe it closely. It marked the first time scientists were able to study it with sophisticated and developed technology. The high-quality images returned by the probes were the first of their kind, providing a fascinating insight into Halley and proving that its core is a solid mass primarily composed of dust and ice. Five spacecraft from the USSR, Japan, and the European Space Agency journeyed to Comet Halley. ESA’s Giotto obtained close-up photos of the comet’s nucleus. Halley being large and active, with a well-defined and regular orbit, was a relatively easy target for Giotto and the other probes.