A comet with a long, trailing tail appeared on Byeol-maru’s screen, and Byeoli spoke up cheerfully.
“Hyeongseop, this is a special visitor. It’s Halley’s Comet, one that swings by near Earth just once every 76 years.”
“76 years? Why does it take that long?”
“Every comet follows a different path, an orbit, around the Sun. Halley’s Comet traces a long, stretched-out oval orbit, swooping in extremely close to the Sun before traveling all the way out past Neptune and back again. That whole round trip takes about 76 years.”
Hyeongseop imagined the comet traveling that enormous, stretched-out loop.
“So a person might only ever see it once in their whole life.”
“That’s right. If you’re lucky, you might catch it once as a child, and if you live a very long life, maybe once more when you’re older. That’s why people all over the world get so excited and look up at the sky every time Halley’s Comet appears.”
“How do people even know in advance when it’s coming back?”
“Scientists have been observing Halley’s Comet’s path for a very long time. Records going back thousands of years even mention the appearance of what was likely this very comet. Using those records, scientists calculated its orbit precisely enough to predict exactly when it will return next.”
“So when’s the next time it comes back?”
“It’s expected to pass near Earth again around the year 2061. Babies born today might get to see it once they’re grown.”
“Why does the comet’s tail stretch out so long like that?”
“A comet is a clump of ice and dust. As it gets closer to the Sun, its surface starts melting, releasing gas and dust into space. Solar wind pushes that released material away, always in the direction opposite the Sun. So no matter whether the comet is approaching or leaving the Sun, its tail always points away from it.”
“So does the comet get a little smaller every time it passes by?”
“Exactly. Every pass melts a bit more of its surface away. Over an extremely long time, it could eventually melt away completely or break apart. Halley’s Comet will likely keep returning for tens of thousands of years, but it won’t stay exactly the same forever.”
Hyeongseop thought the comet’s 76-year round trip to the far edge of the solar system and back felt like a mail carrier delivering an extremely long letter. He found himself wondering what he might look like, looking up at this same night sky, the next time Halley’s Comet came around.
How Much Did You Remember?
- How often does Halley’s Comet return?
- Why does a comet’s tail always point away from the Sun?
- When will Halley’s Comet return next?
- What happens to a comet with each pass?
(Answers: 1. Every 76 years. 2. Solar wind pushes gas and dust away. 3. Around 2061. 4. Its surface melts a little and shrinks.)
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