All About Halley’s Comet

Written by Priscilla Clarita

4/26/20224 min read

Brief HistoryEnglish astronomer Edmond Halley believed that comets can only make one pass through the solar system. However, he later discovered similarities in bright comets’ orbits and suggested that in 3 different years these comets were making their way back due to Isaac Newton’s theories of gravitation and planetary motions. His prediction about the comet’s return happened 16 years after his death which led to the periodic comet being named after him. Since then, Haley’s comet has been connected to ancient observations, featured in the Bayeux tapestry, and used by the European Space Agency’s Giotto to study from various vantage points. (Barnett, 2020)

Origin and Orbit
Originating from the Oort Cloud, a sphere of cometary bodies far from the Sun, Halley Comet orbits every 75 years and will make its return in 2061. The comet first appeared in 1531, followed by 1607 and 1682, and unfortunately returned 16 years after Halley died in 1758. Interestingly, in 1910, the comet was captured for the first time when it flew about 13.9 million miles (22.4 million kilometers) from Earth. It has a highly-elliptical, retrograde (opposite direction from planets) orbit, 0.6 AU perihelion (nearest point from the sun) placed between orbiting Mercury and Venus, 35 AU aphelion (farthest distance from the sun) that shares the same distance as Pluto and has one of the highest velocities when compared to that of Earth and the Solar System.

There are only 54 Halley-type comets observed till now. With its orbit coming close to Earth in 2 places, it is the parent body of two meteor showers: the Eta Aquarids in early May and Orionids in late October. However, an observation in 1986 showed that the Eta Aquarid may not have come from the comet itself.

Structure, Composition and Lifetime
A bright ion tail formed from the knocking of sublimating gas jets is known as a coma (small atmosphere) and spans 100,000 km of distance consisting of volatiles like water, methane, ammonia, and carbon dioxide. Despite its immense size, the comet’s nucleus is relatively small with its dimensions being 15 km long, 8 km wide, and around 8 km thick. It has a low mass of 1014 kg (242.5 billion tons) and an average density of 0.6 g/cm3. Observations have shown that its nucleus consists of 80% water vapor, 17% carbon monoxide, and 3-4% carbon dioxide with hydrocarbon traces, although the latest updates mentioned that it consists of 10% carbon monoxide and traces of methane and ammonia. Dust particles are a mixture of carbon-hydrogen-oxygen-nitrogen (CHON) compounds common in the outer Solar System and silicates found in terrestrial rocks.

Halley’s Comet loses around 3-10 feet (1-3 meters) from the surface of its nucleus in each orbit as it ages. The comet starts to dim, loses all ice inside its nucleus, its tail begins to disappear, and it evolves into a dark mass of rocky material and eventually into dust. Did you know that it has lived for at least 16,000 years with 1,000 trips around the Sun?

Though it is impossible to be studied deeper since it took decades until it gets close to Earth again, scientists tend to compare it with other small space bodies like the Rosetta probe between 2014 and 2016, which concludes that Halley’s Comet has a different kind of water than on Earth. It is predicted that in 2061, it will be on the same side as the Sun and will be brighter than in 1986 with a magnitude of -0.3 (Howell, 2017).

Myths and Superstitions
The Babylonian scribes mentioned the comet’s return in 164 and 87 BCE. The comet also appeared periodically before the 1066 England invasion by William the Conqueror, making King Harold of England take it as a bad omen. Hence, he made William and his forces visualize it as a sign of victory. On the other hand, throughout the Middle Ages, its appearance in the night sky was seen as a herald of bad news. The comet's appearance potentially meant that either a person of royal standing had died or an era of continuous dark days was approaching. Though this view of the comet has disappeared with the development of modern astronomy, many people still hold onto the “doom and gloom” concept related to the comment. They believe the comet will strike Earth and trigger an extinction-level event proving to be a threat to humanity.

Overall, Halley’s Comet was invented due to a discovery by Edmond Halley. Orbits every 75 years despite many myths and superstitions being made regarding their return to the Earth, it has a highly-elliptical, retrograde orbit, perihelion, aphelion, bright ion tail and large size yet a tiny nucleus, as well as one of the highest velocities in the Solar System. Moreover, its nucleus contains water, carbon, methane, ammonia, oxygen, nitrogen, carbon dioxide and carbon monoxide. There are more interesting things for people to dig in, right? So have you, or your families and friends, seen this before? But if not, do you want to see it someday in the future? Well, don’t forget to catch up on the latest updates from the National Aeronautics and Space Administration by around July 28, 2061!

Department of Physics and Astronomy at the University of Rochester, n.d.


European Space Agency, 1986