Halley's Comet
What is Halley's Comet?
Comets· Nucleus 11 km. The first comet whose return was successfully predicted. It comes back to the Sun about every 76 years, and its next visit is in the summer of 2061.
Past visits and the next return
Orbit and period
| Nucleus | ~11 km |
|---|---|
| Period | 76 yr |
| Next perihelion | July 2061 |
Figures are representative approximations. Source: compiled from NASA and IAU public data.
Christmas 1758, when Halley's comet came back on time
On the night of 25 December 1758, Johann Palitzsch, a farmer and amateur astronomer in Saxony, Germany, found Halley's Comet again with his own telescope, weeks ahead of the professional observatories. It was the first time a predicted comet had actually returned, and it showed the public that Newton's law of gravity could forecast events in the sky.
The date of return was pinned down more closely by Alexis Clairaut in France. He reasoned that the gravity of Jupiter and Saturn would slow the comet, and he predicted its closest approach to the Sun for mid-April 1759. The real date was 13 March, about a month off. Nicole-Reine Lepaute and Joseph Lalande shared the long calculation.
In 1910 Earth passed through the comet's tail. When it became known that the tail contained a poisonous gas called cyanogen, newspapers stirred up fear, and some people bought 'comet pills' and gas masks. In reality the tail was far too thin to do anything. Halley's Comet passed its farthest point, about 35 AU from the Sun, in December 2023 and is now on its way back.
The comet in depth
Halley's Comet is the object that first showed that comets come back. In 1705 the English astronomer Edmond Halley argued that the comets seen in 1531, 1607 and 1682 were one and the same, and he predicted it would return around 1758. Halley died in 1742, but the comet came back as he had said and was named after him.
People have been recording Halley's Comet for a very long time; every return since 240 BC is on record. Its appearance around the Battle of Hastings in England in 1066 is even stitched into the Bayeux Tapestry, a long embroidered cloth. Because it returns about every 76 years, a person can see it once or twice in a lifetime.
When Halley returned in 1986, spacecraft from several countries went out to meet it. Europe's Giotto came within about 600 km of the nucleus and photographed it. The nucleus was peanut-shaped, 15 km long and 8 km wide, and so dark that it reflects only 4 percent of sunlight. Soviet and Japanese probes observed the comet too.
Dust shed by the comet still reaches Earth as meteor showers, because Earth passes near Halley's orbit twice a year. The Eta Aquariids in May and the Orionids in October both come from its dust. In the orbit view you can see its long orbit reaching from beyond Neptune's path to inside Venus's.
Frequently asked
- How long is the orbital period of Halley's Comet?
- The period of Halley's Comet is 76 yr.
- When does Halley's Comet return?
- The next perihelion of Halley's Comet is July 2061.
- In one line, what is Halley's Comet?
- Comets — The first comet whose return was successfully predicted.
Related
Figures are representative approximations. Simulated positions use J2000 mean elements.