Earth: rotation, orbit, and seasons
Spin gives day/night. Orbit gives the year. Tilt gives the seasons.
Rotation. Earth spins on its axis from west to east. One full rotation = . As a result:
- Sun appears to rise in the east, set in the west.
- Day on the side facing the Sun; night on the opposite side.
Orbit. Earth travels around the Sun in an approximately circular orbit. One full orbit = (hence leap years).
Axial tilt (). Earth's spin axis is tilted relative to its orbit. As Earth orbits, different hemispheres receive direct sunlight at different times of year:
- Hemisphere tilted TOWARD the Sun: SUMMER (longer days, sun higher, more direct rays).
- Hemisphere tilted AWAY: WINTER.
Equinoxes. Twice a year (March, September), neither hemisphere is tilted toward the Sun β day and night are roughly equal globally.
Solstices. Once at maximum tilt each way (June: Northern summer; December: Northern winter).
Why does the Sun feel hotter at noon? Sun is overhead β direct rays hit a small area β high intensity. In morning/evening the rays hit at a low angle β spread over a large area β less intense.
- Rotation: 24 hours, day/night.
- Orbit: 365.25 days, one year.
- Tilt : seasons.
- Direct rays: hot. Glancing rays: cooler.