Will spun in place, holding a basketball in one hand and a baseball in the other.
"If the basketball is the sun and the baseball is Earth, the baseball should go around the basketball," he told himself.
"But why can't we see the sun all the time?"
Dizzy, he lay down on his bed and stared at his homework.
"All I know is that it gets dark at night—not why!"
Will tried to focus on the worksheet, but he soon dozed off.
When he opened his eyes, he was amazed to see Earth and the moon before him.
"Cool!" he exclaimed, pulling his phone, QT, out of his pocket. "Am I on a spaceship?"
"Yes," QT replied. "Earth is beautiful, isn't it?"
"It sure is. But why can I see only one side of it?" Will asked. "And of the moon too?"
"That's because the sunlight's coming from the left, so it can't shine on the opposite side.
On the side that's lit right now, it is day. On the dark side, it is night.
If you look carefully, you can see the lights of big cities."
"I see them! But when the sun rises, the sides will switch, right?"
"What you call the sun rising is not exactly correct.
We don't experience day and night because the sun moves, but because Earth spins on its axis."
Will was confused. "Its axis? What's that?"
QT explained, "An axis is an imaginary line that goes through Earth's poles. I'll show you."
QT shot a beam of light at the ship's controls, and a screen lit up one wall.
"Earth rotates on its axis, spinning like a top, once every 24 hours.
Although the rotation is too slow for us to see in real time, here's a video of the last 24 hours, sped up," QT said.
"The planet is spinning!" Will observed.
"But to us on Earth, it looks like the sun is rising in the east, moving across the sky, and setting in the west."
"Exactly," QT replied. "The view from Earth is quite different from the view from space.
Watch the moon in this next video, and you'll see what I mean," QT went on.
"The moon's shape appears to change—what we call the phases of the moon—but it actually stays the same.
What changes is how much of it we can see.
Half the moon, the side facing the sun, is always lit.
But because the moon orbits around Earth, we can usually only see part of the lit side."
"Oh . . . ," Will said, watching closely.
After the video finished, he asked, "So where the moon is in its orbit determines how much of it we can see?
That creates the phases of the moon?"
"You've got it," QT answered. "But I want you to see something else.
Take another look at Earth out there. Doesn't it look like it's tipping a little?"
Staring at the planet, Will exclaimed, "Hey! It does."
"Earth is tilted by about 23.5 degrees; that means it's not straight up and down.
If we move farther out, you'll see what I mean," QT said.
As they zoomed through the solar system, Earth got smaller and smaller, and the sun came into view.
Will gasped. "It's enormous! And bright!"
"It sure is. It looks small from Earth because it's very far away, about 150,000,000 kilometers.
So the orbit is a long trip. It takes about 365 days to orbit the sun once—"
"That's a year," Will interrupted.
"Yes, it is. Earth's tilt causes the seasons. I'll show you a diagram," QT said.
The screen lit up, showing Earth's orbit of the sun.
"The planet is always tilted the same way,
so the northern hemisphere is pointed toward the sun for part of the year, and the southern hemisphere for another part."
"The seasons in the northern and southern hemispheres are always opposite?" Will asked.
"Right. The hemisphere that's tilted away from the sun experiences winter, and the one that's tilted toward the sun experiences summer.
Right now it's December—winter in the northern hemisphere, where you live.
See how little direct light it's getting compared to the southern hemisphere?
There it's summer because it's getting a lot of direct light.
When the northern hemisphere is tilted toward the sun, it gets much more sunlight, so it's summer.
For spring and fall, neither hemisphere is tilted toward the sun, so the weather is the same."
Will thought for a moment. "Is that why the days are longer during the summer?
Because the northern hemisphere is tilted toward the sun?"
"Absolutely. That's what causes the 24-hour days in the Arctic.
And the Antarctic doesn't see the sun at all, causing 24-hour nights," QT said.
"But I'd better turn the ship around now.
We don't want to be floating out in space forever, do we?"
"No." Will grinned. "I've got basketball practice tomorrow!"
The spaceship started moving back toward Earth, but as they flew past the sun, the ship swerved.
"What's going on?" Will asked. Red lights on the controls were blinking, and a warning bell was ringing.
"We might have gotten too close to the sun," QT said, sounding worried.
"Its gravity is pulling us in!" The ship was going faster and faster, straight into the sun.
Will covered his eyes with his hands to protect them from the blinding rays.
When he lowered his hands, squinting at the bright light, his dad was standing by the bedroom door with his hand on the light switch.
"Why was the light off?" he asked Will.
"I was just napping," Will replied, crawling out of bed.
"Thanks for waking me up. I have to finish something."
He picked up his homework and quickly answered the questions.
"That wasn't so hard," he thought, putting away the basketball and baseball.