Understanding Earth's Seasons

Scientific Explanation of Seasonal Change Due to Planet Tilt

Jun 16, 2008

Explaining why the earth has seasons is a basic science concept everyone should be able to do with little hesitation. However this is one basic fact most cannot explain.

What causes seasons is one of the least understood science facts today. Graduating college students are asked, what causes seasons? Their answers are 90% incorrect.

Typical answers are:

Seasons are based on the earth’s distance from the sun. The earth is closest in the summer and farthest in the winter.
Seasons are based on how close the sun moves towards the earth. It is closest in summer.
Seasons are based on how early the sun rises in the morning and sets in the evening.

Science Misconceptions about Seasons

These are not correct. How does a person go through 16 years of education and not understand earth’s seasons? The reason is due to their prior knowledge and experiences. Where does this prior knowledge and experiences originate? They come from:

Parents
Teachers who do not understand this themselves
Watching movies
Watching TV
Reading books containing incorrect facts
Students being told the answer so they could memorize it for a test

These are the leading causes why college graduates do not know what causes earth’s seasons.

Why Earth has Four Seasons

The answers college graduates gave are somewhat correct; however they are wrong. The cause of earth's four seasons is due to the “tilt of the Earth.”

The earth is tilted at 23.5 degrees and as the earth rotates around the sun, the tilt is always in the same direction. If the tilt changed direction, the earth would wobble on its axis like a spinning top slowing down to a stop.

As the earth rotates around the sun, it does so in an elliptical orbit. The sun is not in the center of the orbit, it is off to one side of the center.

As the earth rotates around the sun, it is summer on the part of the earth north of the equator (Northern hemisphere). This is when the earth is furthest from the sun and the earth is tilted towards the sun.

It is winter in the Northern hemisphere, when the earth is closest to the sun and the earth is tilted away from the sun.

Proving the Four Seasons

To prove this is true, the following items are needed to conduct an experiment:

1 flashlight
1 globe
2 people

The experiment:

Select a large room to conduct the experiment.
The person holding the flashlight (Sun) stands to one side of the center of the room, with the flashlight pointing directly at the globe.
The person holding the globe ensures it is tilted at 23.5 degrees (close will work).
Turn off the lights.
The person with globe moves around the sun in an elliptical orbit starting in the winter position (furthest from sun and globe tilted toward the sun). Notice the sun light is concentrated north of the equator (this is why it is summer).
The person with the globe moves to the winter position, which is opposite the winter position (closer to the sun and globe tilted away from the sun). Notice the sun light is concentrated south of the equator.
Try the spring and fall positions (half way between the winter and summer positions). Notice the sun light is concentrated on the equator (equal sun light north and south of the equator).

Children may ask about the seasons south of the equator and they are opposite in the Southern hemisphere (south of the equator). As seen in this investigation, seasons are casued by the tilt of the earth. So when they graduate from college they will be able to answer the question correctly.

The copyright of the article Understanding Earth's Seasons in Homeschooling is owned by David R. Wetzel. Permission to republish Understanding Earth's Seasons in print or online must be granted by the author in writing.