(EMS) The Reason for Seasons Lesson

The Reason for Seasons

The Earth's orbit around the sun is NOT a perfect circle. It is an ellipse, which looks more like a flat oval. The seasons are not caused by how close the earth is to the sun. In fact, the earth is closest to the sun around January 3 (brrrr) and farthest away from the sun around July 4 (whew it's hot). These are estimates because seasons do not always happen at the same time everywhere on Earth.

What is an Ellipse?
An ellipse is not a circle, and it's not an egg. It's kind of like an oval, but not quite. It's an elongated oval. 

Four Seasons

The seasons are mostly due to the axial tilt of the earth. The change in distance of the earth to the sun is a very minor player.

Be careful though!!!! Make sure you understand why the tilt of the earth causes seasons. It is not because one side is closer.

Earth's Axis

An axis is an invisible line around which an object rotates, or spins. The points where an axis intersects with an object's surface are the object's north and south poles. In this illustration, Earth's axis is represented by the red line. The white circle represents axial precession, the slow "wobble" of the axis.

 

The earth's rotation around the sun determines the seasons. Seasons in the Northern Hemisphere are the opposite in the Southern Hemisphere. Equinoxes occur when parts of the earth experience equal amounts of daylight and dark—in the spring and fall. Solstices occur on days experiencing the most sunlight (summer solstice) and the least sunlight (winter solstice). The Earth revolves around the sun, so sunlight hits different parts of the Earth, causing yearly changes in climates, called seasons.

Review

Earth has seasons because of the (23.5°) tilt of its axis of rotation.

In the Northern Hemisphere, at summer solstice the sun is closest to the North Pole (around June 22).

At winter solstice, the sun is closest to the South Pole (around December 22).

In the Southern Hemisphere, the names are changed.

At equinox, the sun is directly over the equator.

Autumnal equinox is around September 22.

Spring equinox is around March 22.

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