Dear Braelyn,

If I drew a straight line through the Earth to the opposite side of the planet from me, I’d hit a place called Port-aux-Français. That’s an island near Antarctica. Mostly scientists live there.

Right now, it’s 12 PM, or noon, on Friday for me. But those scientists are probably snoozing in their beds. For them, it’s after 12 AM, or midnight, on Saturday. They’re already living in my tomorrow. Weird!

I talked about why that is with my friend David Luftig. He’s a science librarian at Washington State University. Science librarians are experts in two things: science and helping people find information for research and learning.

He told me it’s all because of Earth’s rotation. As the Earth rotates, or spins, the sun shines on one part of the Earth at a time.

“Billions of years ago, there was just a bunch of dust and gas in what is now our solar system,” Luftig said. “All this dust and gas was moving in a counter clockwise direction. Under the weight of gravity, the dust started to clump together to form the sun, the planets and other objects. That’s why the planets revolve around the sun in the same direction and most planets rotate in the same direction. It’s because we all formed from the same stuff.”

Imagine you could poke a giant needle through the north pole and out the south pole. The imaginary line made by your imaginary needle is Earth’s axis. Earth spins on its axis—like a fidget spinner or top.

The Earth completes one full spin on its axis about every 24 hours. So, one day is 24 hours long.

As Earth slowly spins on its axis, different parts of the planet face the sun. So, it’s daytime for me because my side of the planet is facing the sun. But my scientist friends on Port-aux-Français are having nighttime because they’re facing away from the sun.

So, how do we work out how to call each other if our days and nights are opposite?

Humans used to be pretty loosey-goosey about marking time. An early human might have told their early cat, “I’m off to forage, but I’ll be back before it’s dark.”

That worked just fine because they were living in the same place so light and dark happened at the same time. But once humans started connecting with people far away, thanks to technology like telephones and trains, it got more complicated.

So, humans divided the Earth into 24 time zones—one for each hour of the day. The zones are marked by evenly spaced, imaginary lines that run up and down the globe. We can look at maps of those time zones to figure out what time it is all over the world.

But get this: Luftig told me that a day on Earth hasn’t always lasted 24 hours. Because of the way the Earth and the moon pull on each other, it takes the Earth a fraction of a second longer to make a full spin on its axis every year. When the dinosaurs dominated the planet, a day was only about 23 and a half hours.

I guess time really dino-soared back then.


Dr. Universe