Why is a Day on Mercury Longer than a Year? (Captain Curious)

Josh (0:00)

To all the grownups listening, today's episode is a Captain Curious adventure. If your kids enjoy these special episodes, you can download them all and get the first album free at curiouskidseveryday.com/captaincurious.

Why is a day on Mercury longer than a year?

Welcome to Curious Kids Every Day. I'm Josh. How are you doing today? It's so good to hear from you. Hey, do you know what time it is? It's Captain Curious time. Do you remember when we imagined that Captain Curious found a rocket ship and he was launching into space? We found a treasure chest near the sun that had ten slots for space rocks. We need to go find those space rocks. I've been so excited to find out what happens next.

SPEAKER_2 (1:04)

Are you ready to go?

Josh (1:06)

Okay, close your eyes and pretend we're back on the rocket ship.

SPEAKER_2 (1:10)

Are you ready?

Josh (1:12)

Repeat after me. Three, two, one, blast off!

SPEAKER_2 (1:20)

Do you see the earth out the window?

It's getting smaller and smaller. While we're on this rocket ship, you can call me Captain Curious!

Josh (1:49)

All right, I wonder where we're going today. While we're traveling, let's go check the Curious container and see if there's anything new in there.

Today, we've got a birthday cake? No, wait, it's two birthday cakes. Why do we need two birthday cakes? Can you get a pencil and some paper and draw two birthday cakes?

Oh, oh, wait, there's one more thing in here too. It's a time machine. This will help us speed up time. But why would we need to do that today? Well, go ahead and draw two birthday cakes and a time machine so you can help me figure it out, okay? You can make the time machine look however you want in your imagination. Time machines aren't real in real life, so what do you think a time machine would look like?

SPEAKER_2 (2:56)

Oh, look out the window!

Josh (3:09)

A planet is a big round object in space that orbits a star, like our sun. Our solar system has eight planets, and Mercury is the first one. Okay, the ship has touched down. Let's open the hatch and step outside. Now, while we're traveling around in space, we are wearing our special protective space suit. This keeps us safe from extreme high and low temperatures, pressure changes, and any other poisons or toxins that we might encounter.

Mercury's surface is dry, rocky, and dusty. It looks kind of like our moon. The ground is covered in craters, big and small, from space rocks that crash here. Okay, now, what color is the sky on Earth?

But on Mercury, the sky looks completely different. It's black.

SPEAKER_2 (4:27)

Totally black.

Josh (4:29)

Even during the daytime.

SPEAKER_2 (4:31)

Why?

Josh (4:32)

Because Mercury has almost no atmosphere.

Atmosphere is a layer of gases that surrounds a planet, like a giant invisible blanket of air wrapped all the way around it. Earth's atmosphere is what we breathe. It's full of oxygen and nitrogen, but it also does a lot more than just help us take deep breaths. It keeps us warm by holding in heat. It protects us from dangerous space rocks, because most of them burn up before they land. And the atmosphere even makes our sky look blue by scattering sunlight. But here on Mercury, because there's no air to scatter the sunlight, the sky doesn't change color. It just stays pitch black, even when the sun is shining super bright.

Can you close your eyes and imagine if you could see stars during the day on Earth?

Another thing I'm noticing about Mercury is how quiet and still it is. There's no wind, no weather, just rocks, silence, and maybe a hidden space rocket if we're lucky. I wonder where we might find it. Remember, we're looking for 10 total. My spacesuit tells me that it's over 800 degrees Fahrenheit here. Good thing we've got this spacesuit because 800 degrees Fahrenheit is hot enough to melt metal. But let's go to the shadowy side of Mercury, the side where we can't see the sun. I wonder what the temperature is away from the sun. Oh, and when I jump, I jump a lot higher than on Earth. Whoa, that feels weird. Gravity here is about one third as strong as on Earth. So, if you weigh 60 pounds on Earth, you weigh about 20 pounds on Mercury. Hey, can you pretend you're jumping around on Mercury?

Come on, let's go to the shadowy side of Mercury.

SPEAKER_2 (7:14)

Okay, we made it.

Josh (7:16)

We're away from the sun. And guess what? The temperature has dropped down to negative 300 degrees Fahrenheit. That's colder than anywhere on Earth. Do you know why the temperature here gets so hot in the sun and so cold when the sun is gone?