Every Planet Has a Different Day Length

“Another day’s gone by, Hyeongseop. Time for bed.”

“Byeol-i, how long is a day on other planets? Is it 24 hours like on Earth?”

“Totally different! Every planet spins around at its own different speed.”

“Which one has the shortest day?”

“Jupiter. Even though it’s so huge, it only takes about 10 hours to spin all the way around once.”

“It’s that big and it spins that fast?”

“Yep, so on Jupiter, a day would fly by in a flash. You’d barely finish breakfast before it was already night again.”

“What about the longest day?”

“Venus. A single day on Venus takes a whopping 243 Earth days.”

“243 days? That’s basically a whole year in one day!”

“Here’s something even stranger. On Venus, a day is actually longer than a year. It takes 225 days to orbit the Sun once, but 243 days to spin around just once on its own axis.”

“Wait, what? A day is longer than a year?”

“Exactly. Some scientists joke that on Venus, your birthday comes around faster than ‘today’ does.”

“That’s so weird. But why do all the planets spin at different speeds?”

“When planets were first forming, clouds of space dust and rocks clumped together and just happened to start spinning with different amounts of force. After that, unless something else happens, that spin speed pretty much stays the same forever.”

“So Earth’s 24 hours was just an accident too?”

“An accident, but a really lucky one for us. Day and night got split up just right, which is exactly why we can sleep and wake up on a schedule that actually works.”

“I’m glad tonight isn’t a short Jupiter-style night. I really want a good sleep.”

“Exactly. Earth’s 24 hours are exactly right for a good night’s sleep, tonight included.”

Hyeongseop pulled his blanket up to his chin and closed his eyes. Tonight, he felt like he could sleep soundly for exactly one Earth-length night.