Lab 8: Seasons, Solstices and Equinoxes
Part I: The Reasons for the Seasons
Below are three facts about the seasons that we wish to explain. Below the facts are four hypotheses about what might cause the seasons to occur. Your job is to think about each one and figure out which of the four hypotheses are most right and which ones are wrong. Be sure to keep these three facts in mind while going through the lab.
Key facts about the seasons:
I. In northern latitudes, it’s warm in June/July and cool in Dec/Jan, on average.
II. In southern latitudes, the seasons are reversed: it’s warm in Dec/Jan and cool in June/July.
III. It’s warmer at latitudes close to the equator than at latitudes close to the poles (on average).
Hypothesis #1: The Sun-Earth distance changing due to
Earth’s elliptical orbit causes the seasons.
If its orbit were a circle, the Earth would always be the same distance from the Sun. But it’s not. The orbit is an ellipse. As compared to the average Earth/Sun distance, the Earth is sometimes 1.7% closer and at other times 1.7% farther away from the Sun than the average.
Is this difference significant? To answer this question, it helps to be able to refer to a scale model of the Sun/Earth system. Recall the scale model of the solar system we made in Lab 1. We made the size of the Sun and Earth and the distance between them all smaller by the same factor: 1010. Let’s repeat these calculations for the Earth-Sun system.
Sun diameter: 1.4 × 106 km → scale model Sun diameter = 14 cm
To get the above, remember that we divide by the scale factor to shrink the normal size:
