The changing of seasons has mystified man for ages. The amount of hypotheses on why they change is plentiful. When sorting through the theories, there are two that are highly agreed upon. One theory is that seasons are caused by the fluctuation of the distance between the Earth and the Sun. The second theory is that the combination of the Earth's axis tilt and its pattern of revolution around the Sun cause the change of seasons. Only one of these suppositions is correct.

By executing on-line research and a series of experiments, we have concluded that the fluctuation of seasons is caused by the combination of the Earth's axis tilt and its pattern of revolution around the sun. Look at the image below to better understand the change of seasons.

You should notice that the Earth's tilt causes sunlight to strike more on some areas and less on others.

The other popular theory, that seasons are caused by the changing of the distance between the Earth and the Sun, is moderately correct. This assumption is referred to as the Milankovitch Cycle. Before we explain this theory, you need to understand the definitions of several words. An elliptical orbit is an orbit that is not perfectly circular, such as the Earth's orbit. When the Earth reaches perihelion, it is at the point where its orbit is closest to the Sun. Aphelion is exactly the opposite; when the Earth is furthest from the Sun. The Milankovitch Cycle states that the Earth's orbit is not constant. Over a period of 90,000 to 100,000 years, the Earth's orbit expands into a longer ellipse, and then returns to a more circular orbit. At the maximum orbital irregularity, the Earth would receive 20-30% more solar radiation at perihelion than at aphelion. This increase in solar radiation causes a growth in the surface temperature on Earth, but only by a few degrees Celsius.

Along with research, we conducted an experiment to further prove the axis tilt theory. This was accomplished by the use of a small spotlight, a group of solar cells, an electricity tester with clamping leads, a meter stick, and a protractor. The solar cells acted as the Earth, and the spotlight as the Sun. Pictures of the materials are below.

We connected one end of the leads to the top of the cell, and the other end to the tester. We then moved the cell at a distance of 40cm (our choice), tilted it at 23.5°N, simulating winter for the Northern Hemisphere, and recorded the voltage. Then, we angled the cell at 90° (straight up and down), simulating a solstice, and measured the voltage. The end results were as we had predicted. When the cells were tilted toward the Sun to simulate winter, there was less energy received than when we tilted the panel to simulate the solstice. There was exactly one volt difference, thus proving the axis tilt and Sun revolution rationale correct. Here is an illustration of how we tested theory #2.

We executed another experiment based on the Milankovitch Cycle theory, to further explain that it is incorrect. To accomplish this, we used the same materials from the first experiment, except for the protractor. To get the different distances between the Earth and the Sun, we worked it as a proportion. The work is shown below.

You will notice that the same amount of sunlight has to cover a different area. This causes a change of temperature on numerous areas of the earth, contributing to the change of seasons. This concludes our proposal on why and how seasons change on earth. We hope that this report has expanded your knowledge on our home planet, and exposed you to the new horizons about your life on earth. If you would like to get more information on this project, visit this site: