Rocket sets a globe on the roof table and aims a flashlight at it. "Watch the equator," he says.
The beam makes a small, bright circle. He tilts the flashlight toward the top of the globe.
The circle stretches into a long, dim oval across the far north.
"What do you notice?" Raven asks. "The same light covers more ground up there. So each spot gets less."
Nova rotates the globe slowly. "The Earth is a sphere. Sunlight meets it at different angles," she says.
"And the axis leans. Try pointing the top of the globe toward the flashlight, then away."
Rocket tries it. "Summer," he says, as the north brightens. "And now winter."
NASA explains that the Sun does not heat the Earth evenly. Because the Earth is a sphere, it heats the equator more than the poles.
Only the point directly under the Sun receives full strength sunlight.
From the equator toward the poles, the Sun's rays meet the Earth at smaller and smaller angles.
The same light gets spread over larger and larger areas, so each square meter receives less.
NASA compares the energy received at different latitudes on the equinoxes, in March and September.
| Latitude band | Energy compared with the equator |
|---|---|
| The tropics (0 to 23.5 degrees) | About 90 percent |
| The mid-latitudes (45 degrees) | Roughly 70 percent |
| The Arctic and Antarctic Circles | About 40 percent |
The Earth spins once a day around an imaginary line through its center, called its axis. That spin gives us day and night.
NASA explains that the axis does not stand straight up. It is tilted off vertical by about 23 degrees.
As the Earth orbits the Sun, the tilt always points the same way. So different parts of the Earth get the most direct rays at different times.
Around June the North Pole tilts toward the Sun. It is summer in the Northern Hemisphere, with more direct sunlight and longer days.
Around December the South Pole tilts toward the Sun. Then it is winter in the Northern Hemisphere.
Many people think summer comes when the Earth is closest to the Sun. NASA says that is not the cause.
The Earth is actually closest to the Sun in January and farthest in July. The tilt, not the distance, makes the seasons.
| Statement | True or false? |
|---|---|
| The Earth's axis is tilted by about 23 degrees. | ? |
| Summer happens because the Earth is closest to the Sun. | ? |
| When the North Pole tilts toward the Sun, it is summer in the Northern Hemisphere. | ? |
| The Earth spins around its axis once a day. | ? |
Excellent modelling. Tomorrow's Station Lab tests Rocket's roof puzzle: why land and water warm differently.