Earth's Seasons and Tilt
Overview
This lecture reviews how Earth's tilt and orbit cause the seasons, explains how to identify each season, and clarifies the differences between hemispheres.
Earth's Tilt and Orbit
- The Earth's axis is tilted relative to its orbit around the Sun.
- The combination of Earth's tilted axis and its orbit causes the seasons.
- The direction of Earth's tilt stays nearly constant throughout the year due to slow precession.
Identifying Seasons in the Northern Hemisphere
- It is summer in the northern hemisphere when the North Pole is tilted towards the Sun.
- It is winter when the North Pole is tilted away from the Sun.
- Spring and fall occur when the Earth's tilt is neither towards nor away from the Sun.
- The sequence of seasons in order is: summer, fall (autumn), winter, spring.
Understanding Season Placement
- To determine the seasons, first locate summer (north pole tilted towards the Sun).
- After identifying summer, the next position is fall, followed by winter, then spring.
- Confusing the order of the seasons is a common mistake.
Seasons in the Southern Hemisphere
- Seasons in the southern hemisphere are always the opposite of those in the northern hemisphere.
- If it is summer in the north, it is winter in the south (and vice versa).
- For spring in the north, it is fall in the south; for fall in the north, it is spring in the south.
Key Terms & Definitions
- Tilt (of Earth's axis) — The angle between Earth's rotational axis and its orbital plane, causing seasonal changes.
- Precession — The slow wobble of Earth's rotational axis, negligible within a human lifetime.
- Autumn — Another word for "fall," the season after summer and before winter.
Action Items / Next Steps
- Review the order of the seasons and their causes.
- Make sure to recognize that "autumn" and "fall" mean the same season.
- Prepare to identify seasons based on Earth's tilt and position in orbit for future assessments.