Space Cycles Seasons

A regular change in temperature that repeats itself every year

Words to know: Axis - imaginary line around which Earth spins, causing day and night, and that is drawn from the north geographic pole through Earth to the south geographic pole

Words to know: Rotation - spinning of Earth on its axis, which causes day and night; it takes 24 hours for Earth to complete one rotation

Words to know: Revolution - the motion of Earth around the Sun, which takes about 365 1/4 days, or one year, to complete

Words to know: Orbit - curved path followed by Earth and other planets as they move around the Sun. They are not perfect circles. Their shape is called an ellipse.

The Earth’s Tilt The Earth's axis is tilted by 23.45°

As the Earth moves around the Sun, the axis always points in the same direction.

This means that, during part of the year, the northern part of the Earth will lean toward the sun, and during other parts of the year the southern part of the Earth will lean toward the sun.

Earth-Sun Relations

When the Northern Hemisphere is tilted toward the sun it receives more direct rays of light. The light is more concentrated. This causes the temperature of the Northern Hemisphere to increase more than the temperature of the Southern Hemisphere which receives less direct rays of light.

When the Sun is higher in the summer sky, the sunlight is more concentrated …. Concentrated beam of Summer sunlight … than in winter, when the Sun is lower in the sky, and the sunlight is more diffuse. Diffuse, “spread-out” beam of Winter sunlight

The ground receives more energy (more heat) per square meter in the summer because the light energy is more concentrated due to the angle at which the sun’s rays strike the Earth.

So, seasons are caused the tilt of the Earth’s axis

Remember: The seasons are the result of the tilt of the Earth's axis combined with its revolution around the sun. If the tilt of the Earth's axis was 0° there would be no change in how the rays from the sun strike the Earth throughout the year. There would be no seasons.

The Earth's seasons are not caused by the differences in the distance from the Sun throughout the year.

The seasons are the result of the tilt of the Earth's axis combined with its revolution around the sun. I know this is a repeat, but it is important that you understand this idea. Many Americans, including Harvard graduates, do not know what causes seasons!