Despite making its appearance only once every roughly 75 years, Halley’s Comet is perhaps one of the most famous objects in the night sky. It last passed by Earth in 1986, and both astronomers and skywatchers are eagerly anticipating its return in 2061.
When Halley’s Comet reappears in Earth’s skies, it will likely be a spectacle that will yet again captivate much of the world — and potentially worry some. But, since we still have some time before Halley’s Comet returns, let’s dive into what makes this comet so special, the incredible journey it’s on, and what we can expect when it once again passes near Earth.
What Is Halley’s Comet?
Halley’s Comet, officially designated 1P/Halley, is a short-period comet (less than 200-year orbit around the Sun) that is regularly visible from Earth about every 76 years. Halley’s Comet is the only known short-period comet that is consistently visible to the naked eye, as well as the only short-period comet that can appear twice in a human lifetime. And during the comet’s last approach in 1986, it become the first comet in history to be studied in detail by spacecraft.
The comet is named after the English astronomer Edmond Halley. In 1705, Halley found that three bright comets reported in 1531, 1607, and 1682 all had similar orbits. He proposed that these three comets were actually the same comet, and then correctly predicted it would again return to the sky in 1758. Unfortunately, Halley died in 1742, long before the comet’s reappearance.
Read More: 20 Things You Didn't Know About Comets
How Big Is Halley’s Comet?
Halley’s Comet isn’t just a spectacular sight; it’s also a remarkable object in terms of its physical traits. The comet's nucleus is covered in craters and has an irregular shape, measuring roughly 9 miles (15 kilometers) long, 5 miles (8 km) wide, and 5 miles (8 km) thick. Despite its relatively modest size, the comet's coma — the cloud of gas and dust surrounding its nucleus — can expand to hundreds of thousands of miles in diameter when it is near the Sun, making it visible from Earth even without binoculars or a telescope.
Halley’s Comet is a dirty snowball made of a mixture of volatile ices, such as water, carbon dioxide, ammonia, and methane, along with plenty of dark dust and rocky material. As it approaches the Sun, the heat causes the ices to sublimate (turn directly from solid to gas), creating the spectacular tail that comets are known for. This tail can extend millions of miles across space, and it always points away from the Sun due to the solar wind.
When Was Halley’s Comet Last Seen?
Observations of Halley’s Comet go back to at least 240 B.C., but it was last seen in 1986. This latest appearance was particularly significant because it was the first time humanity had the technology to study the comet up close. Scientists sent an international fleet of five spacecraft to intercept and investigate the comet during its trip through the inner solar system, including the European Space Agency’s Giotto probe, which provided the first close-up images of a comet’s nucleus.
Unfortunately, the 1986 apparition was not as visually spectacular as the comet’s previous appearances, and it was possibly the worst view in more than 2,000 years. This is mainly because the comet was on the opposite side of the Sun from Earth during its closest approach, making it less visible. Plus, excessive light pollution didn’t do observers any favors.
Despite this, the scientific data gathered during this latest pass was invaluable. It provided insights into the composition and structure of the comet and confirmed many theories about the nature of comets in general.
Read More: Where Comets Come From
When Will Halley’s Comet Return?
If you missed the comet’s last appearance (perhaps, like me, you weren’t alive yet), don’t worry. You’ll hopefully have another chance. Halley’s Comet will make its next closest approach to the Sun, known as reaching perihelion, in July 2061. And this time, the comet will be much closer to Earth than it was in 1986, offering a far better view for stargazers and astronomers alike.
In 1986, Halley’s Comet peaked at an unremarkable magnitude 2.4. In 2061, it is expected to peak at magnitude –0.3, making it appear some 12 times brighter than last time. (When it comes to astronomical magnitudes, the more negative the number, the brighter the object.)
The next visit by Halley’s Comet could be one of the most observed and studied events in the history of astronomy. Advances in technology since 1986 mean that scientists will have the opportunity to gather even more detailed data, potentially answering some of the lingering questions about the comet's long-term behavior and evolution. Then again, missions to comets have become increasingly routine over the past few decades, so perhaps Halley’s Comet received the most research love it will ever get during its last visit.
When Will Halley’s Comet Die?
Like all comets, Halley’s Comet is slowly losing material each time it passes close to the Sun. As its volatile ices sublimate, it loses mass, and its nucleus gradually shrinks. Researchers estimate that with every orbit around the Sun, the diameter of Halley’s Comet shrinks by some 6 to 20 feet.
While it’s difficult to predict exactly when Halley’s Comet will become inactive, it’s estimated that it could last for another few hundred thousand years before it loses too much mass to continue its characteristic bright displays.
But this doesn’t mean the comet will completely disappear. The remains of its nucleus will continue to orbit the Sun, but without the spectacular tail and coma that make it so recognizable today. However, some research suggests that Halley’s Comet may collide with another object or be entirely ejected from the solar system in as little as the next 10,000 years or so.
From being depicted in ancient manuscripts to inspiring scientific revolutions, appearances of Halley’s Comet have always been moments of awe and wonder. Whether you’re an avid astronomer or just someone who loves the night sky, Halley’s Comet offers a rare opportunity to witness a piece of human history in motion. Mark your calendars for 2061!
Read More: The First Interstellar Comet Could Disintegrate When it Gets Close to the Sun
Article Sources
Our writers at Discovermagazine.com use peer-reviewed studies and high-quality sources for our articles, and our editors review for scientific accuracy and editorial standards. Review the sources used below for this article:
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ESAThe Visibility of Halley's Comet
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Jake Parks is a freelance writer and editor who specializes in covering science news. He has previously written for Astronomy magazine, Discover Magazine, The Ohio State University, the University of Wisconsin-Madison, and more.
