The Simulation
Earth's axis is an imaginary line through its poles. It is tilted about 23.5 degrees from upright. The red dot is at 40 degrees north, near the latitude of New York or Madrid. These views show Earth on opposite sides of the Sun near the June and December solstices. The axis points the same way in both views. Pick Summer or Winter, then press Start the day to watch one full rotation.
Switching seasons shows Earth on opposite sides of the Sun. Earth's axis keeps the same tilt and direction. Measurements are approximate. The dashed latitude path shows the far side of Earth.
Learn more: What about the other half of Earth? Flipped seasons, and a surprise about distance Tap to read
Seasons are flipped south of the equator. When the North Pole leans toward the Sun, the South Pole leans away. Near the June solstice, it is summer in New York but winter in Sydney, Australia.
Earth's axis points nearly the same way in space throughout the year. What changes is Earth's position as it revolves around the Sun. At the June solstice, the North Pole leans toward the Sun. At the December solstice, it leans away. At the March and September equinoxes, neither pole leans toward the Sun.
At the red dot, summer sunlight strikes the ground more directly, so the same beam covers a smaller patch. In winter it arrives at a lower angle and spreads over a larger patch. Each small area receives less energy. More hours of daylight also give the ground more time to receive energy in summer.
Earth is actually a little farther from the Sun during northern summer than during northern winter. The main cause of seasons is Earth's tilt as it orbits the Sun, not the small change in its distance from the Sun.
Model notes: The orbit diagram is a perspective view, not to scale. Daylight is rounded to whole hours. The model uses the Sun's center and leaves out atmospheric bending of light. The sky window is a simplified view of the Sun's apparent path. Earth's rotation, or spin on its axis, causes day and night; a hemisphere is half of Earth.
Science references: NASA: What Causes the Seasons? and National Weather Service: Seasons.