Chapter 14 Section 3 What causes the seasons? Objective: Explain what causes the change of seasons

Why the Seasons Change As you learned earlier, Earth’s axis is tilted at 23 ½°. The North Pole of Earth points toward Polaris, the North Star. The axis always points in the same direction as Earth moves in its orbit.

Why the Seasons Change The seasons are caused by a combination of the Earth’s axis and Earth’s movement around the Sun. At one point in Earth’s orbit of the Sun, the North Pole of Earth is tilted toward the Sun. Six months later, the North Pole is tilted away from the Sun. This change in position changes the angle at which the Sun’s rays strike Earth’s surface and is responsible for the change of seasons.

Why the Seasons Change When the North Pole is tilted toward the Sun, the Northern Hemisphere receives the Sun’s rays almost directly. The more direct the rays are, the better that part of the Earth’s surface is heated.

Why the Seasons Change The tilt of Earth’s axis also causes the total number of daylight hours to change. When the North Pole is tilted toward the Sun, the Northern Hemisphere has more hours of daylight than it does of darkness. The combination of more direct rays and longer days warms the Northern Hemisphere. It causes summer in that region.

DESCRIBE What combination of factors causes the change of seasons?

Opposite Seasons When it is summer in the Northern Hemisphere, the Southern Hemisphere tilts away from the Sun. The rays it receives from the Sun are less direct. They are spread out more. There are also fewer daylight hours in that part of the world. In fact, there are more hours of darkness than of daylight.

Opposite Seasons The combination of fewer daylight hours and less direct rays cause that part of Earth’s surface to cool. The lower temperature causes winter in that part of the world.

Opposite Seasons The Northern and Southern hemispheres have opposite season. When the Northern Hemisphere is tilted away from the Sun, it has winter. At the same time it is winter in the Northern Hemisphere, the Southern Hemisphere is tilted toward the Sun and has summer. When summer comes to the Northern Hemisphere, it is winter in the Southern Hemisphere.

2. IDENTIFY If it is summer in the Northern Hemisphere, what season is it in the Southern Hemisphere?

Classwork CHECKING CONCEPTS The North Pole points ___ the Sun during the summer in the Northern Hemisphere. Seasons are caused by the ___ of Earth’s axis.

Classwork THINKING CRITICALLY 3. ANALYZE: If it is summer at the North Pole, what season is it at the South Pole? 4. INFER: Why do you think direct sunlight produces more heat than indirect sunlight?