Seasonal Patterns

In this unit, students explore the phenomenon of seasonal changes. In this lesson, they begin exploring this topic by modeling how sunlight reaches Earth as a result of Earth’s tilt. They use their model to explain why seasons happen in a regular and repeated way, and how length of day and temperature changes are related to the seasons. In the next lesson, students explore how temperature and the presence of heat affects the water cycle.

• As Earth rotates on its axis (the imaginary straight line that Earth rotates around), its axis is not straight up and down. Instead, it is tilted slightly to one side.
• Seasons are times of year that have specific weather patterns and amounts of daylight.
• There are more daylight hours in the summer season than in the winter season. The pattern of changing length of daylight repeats from year to year.

• How does Earth move in the solar system?
• What does it mean that Earth’s axis is tilted? How do Earth’s tilt and orbit around the sun cause seasons on Earth?
• What happens to the position of Earth’s axis as Earth orbits the sun? 
• Why might summer happen in the part of Earth tilted toward the sun? 
• How are seasons different near the equator?
• Why are seasons patterns?
• Is there a pattern in the number of daylight hours each season?

Misconception: Seasons are caused by Earth’s distance from the sun—summer is warm because Earth is closer to the sun. Winter is cool because Earth is farther from the sun.

Fact: Seasons are caused by Earth’s tilt on its axis. Summer happens for the part of Earth tilted toward the sun. Winter happens for the part of Earth tilted away from the sun. The part of Earth experiencing winter is actually slightly closer to the sun than the part of Earth experiencing summer.

Misconception: Seasons are the same everywhere on Earth.

Fact: Different parts of the world experience different seasons. For example, near the equator there are just two seasons: a wet season and a dry season.

Atmosphere: the blanket of air that covers a planet

Collection:  the process of liquid water being stored on Earth’s surface

Condensation: the process of water vapor changing into liquid water

Evaporation: the process of liquid water changing into water vapor, its gas state

Precipitation: the process of water falling back to Earth in the form of rain, snow, sleet, or hail

Season: a time of year that has specific weather patterns and amounts of daylight

Temperature: a measure of heat; measured with a thermometer

Water Cycle:  the circulation of water from a collection to the atmosphere and back to Earth; includes evaporation, condensation, precipitation, and collection

Weather: the conditions of the atmosphere in a particular place at a particular time; includes temperature and precipitation

Seasons happen because of Earth’s motion in the solar system. Remember that Earth orbits the sun. It also rotates on its axis.

But Earth’s axis isn’t straight. It tilts to one side. This means that it leans a little. Earth’s axis is tilted. As Earth orbits the sun, its axis always points in the same direction.

Sunlight hits the part of Earth tilted toward the sun directly. When the North Pole tilts toward the sun, it is summer in the north.

When the North Pole is tilted toward the sun it is summer for parts of Earth north of the equator. But it isn’t always summer in the north. Seasons change as Earth orbits the sun. Different parts of Earth tilt toward the sun throughout the year.

Students carry out two hands-on investigations in this lesson. In the first investigation, students create an Earth-sun model that shows the relationship between Earth’s tilt, its orbit, and seasons on Earth. In the second investigation, students collaboratively analyze data on sunrise and sunset times by month over the course of a year, looking for patterns between the length of day and the season.