Why does Halley's Comet cause the Orionid meteor shower every October?
The shooting stars of late October are dust from a comet last seen in 1986, and some of the dust is over 2,000 years old.
The Orionid meteor shower in October comes from dust left by Halley's Comet. The Orionids are one of two meteor showers associated with Halley's Comet, the other being the Eta Aquariids in May. They are named for Orion, the they seem to come from, and they last about a week in late October, normally peaking around 21 and 22 October. In some years there are 50 to 70 an hour.
Here is how a comet makes a shower. When Halley passes through the inner Solar System, the Sun some of its ice, which lets rock particles break away. Those particles keep following the comet's trajectory. When Earth crosses the stream and the particles enter the upper atmosphere, they glow as . The comet itself does not need to be near: during the shower Earth passes about 23 million kilometres from Halley's orbit and runs into the particles spread along it, which hit the air fast, at about 66 kilometres per second.
Step 1: The Sun warms the comet
Ice and rock particles break away
Step 2: A trail follows its orbit
The particles keep the comet's trajectory
Step 3: Earth crosses the trail
About 23 million km from Halley's orbit in October
Step 4:
Particles glow as they enter the upper atmosphere at about 66 km/s
Halley itself is a famous traveller. It is the only known consistently visible to the naked eye, returning roughly every 74 to 79 years. It last appeared in 1986 and will next appear in mid-2061. In 1705 Edmond Halley understood that its sightings, recorded since at least 240 BC, were the same comet returning. The man who first saw his predicted comeback, on 25 December 1758, was a German farmer and amateur astronomer, Johann Georg Palitzsch.
So an October night's shooting stars are, in a sense, tiny pieces of a comet that people have been watching for over two thousand years.
Try it
A stretched-out orbit
- One orbit takes
- 2.83 years
- Speed now
- 28.7 km/s
- Closest – farthest
- 1.4–2.6 AU
Challenge · Raise the eccentricity to 0.7 and watch where the body moves fastest.
Quiz me
0/3
Recap
Halley sheds dust along its orbit, and Earth crosses that trail each late October.
💡 A trick to remember it · Earth drives through Halley's crumb trail every October, and the crumbs light up as they fall.
Surprising fact · Debris dated to 1266, 1198 and 911 BCE helped make a 2006 Orionid outburst.
Sources (2)
No source, no claim. Every fact in this lesson (14 claims) cites at least one of these.