This cheat sheet explains how Earth's axial tilt and yearly orbit around the Sun create the seasons. Students need this topic to understand why temperatures and daylight hours change during the year. It also helps connect observations such as longer summer days, winter shadows, and opposite seasons in different hemispheres.
The focus is on clear diagrams, key dates, and the cause and effect relationships behind seasonal change.
Earth's axis is tilted about 23.5 degrees compared with its orbit around the Sun. When a hemisphere is tilted toward the Sun, it receives more direct sunlight and has longer days, which creates summer. When a hemisphere is tilted away from the Sun, it receives less direct sunlight and has shorter days, which creates winter.
Solstices mark the greatest daylight differences, while equinoxes happen when day and night are nearly equal.
Key Facts
- Earth's axis is tilted about 23.5 degrees from the line perpendicular to its orbital plane.
- Seasons are caused by Earth's axial tilt and orbit, not by changes in Earth's distance from the Sun.
- A hemisphere has summer when it is tilted toward the Sun because sunlight is more direct and daylight lasts longer.
- A hemisphere has winter when it is tilted away from the Sun because sunlight is less direct and daylight lasts fewer hours.
- The June solstice occurs around June 20 or 21, when the Northern Hemisphere has its longest day and the Southern Hemisphere has its shortest day.
- The December solstice occurs around December 21 or 22, when the Northern Hemisphere has its shortest day and the Southern Hemisphere has its longest day.
- The March and September equinoxes occur when both hemispheres receive nearly equal daylight, about 12 hours of day and 12 hours of night.
- Direct sunlight spreads energy over a smaller area, making it more intense, while angled sunlight spreads energy over a larger area, making it less intense.
Vocabulary
- Axial tilt
- Axial tilt is the angle between Earth's rotation axis and the line perpendicular to its orbit, which is about 23.5 degrees.
- Solstice
- A solstice is a day when one hemisphere has its longest daylight period and the other has its shortest daylight period.
- Equinox
- An equinox is a day when day and night are nearly equal in length around the world.
- Direct sunlight
- Direct sunlight is sunlight that strikes Earth's surface at a high angle and concentrates energy in a smaller area.
- Hemisphere
- A hemisphere is one half of Earth, such as the Northern Hemisphere or Southern Hemisphere.
- Orbit
- An orbit is the curved path an object follows around another object, such as Earth's path around the Sun.
Common Mistakes to Avoid
- Saying seasons happen because Earth is closer to the Sun in summer is wrong because the main cause is Earth's 23.5 degree axial tilt, not distance.
- Thinking both hemispheres have the same season at the same time is wrong because the Northern and Southern Hemispheres are tilted in opposite ways relative to the Sun.
- Confusing solstices and equinoxes is wrong because solstices have the biggest daylight differences, while equinoxes have nearly equal day and night.
- Assuming hotter seasons come only from longer days is incomplete because summer also has more direct sunlight, which delivers more energy per area.
- Drawing Earth's axis tilted in different directions at different points in orbit is wrong because the axis stays pointed in nearly the same direction in space throughout the year.
Practice Questions
- 1 Earth's axis is tilted about 23.5 degrees. If a diagram labels the tilt as 0 degrees, what season pattern would Earth have compared with today?
- 2 On the June solstice, the Northern Hemisphere has about 15 hours of daylight in some locations. How many hours of night would those locations have?
- 3 If a city has nearly 12 hours of daylight and 12 hours of night, is it most likely near a solstice or an equinox?
- 4 Explain why Australia has summer when the United States has winter, even though both places are on the same planet orbiting the same Sun.