The change in the intensity of the Sun’s rays

      Due to the tilt of the Earth’s axis causes the seasons. The changing tilt of Earth relative to the Sun also affects the intensity of the Sun’s rays on different parts of the Earth at different times of the year. First, let’s compare the intensity of the Sun’s rays in the summer vs. winter in northern latitudes on Earth. Figure 2: source: https://media.nationalgeographic.org/assets/photos/000/312/31279.jpg Pay attention to Earth A on the left. Notice how the North Pole is tilted towards the Sun, also notice how the most direct Sun rays (shown in brighter yellow) land above the Earth’s equator in the Northern Hemisphere and how the Sun’s rays seem to just graze the Southern Hemisphere. Now pay attention to Earth B on the right. The North Pole is now pointing away from the Sun. Notice now how the Sun’s most direct rays fall below the Earth’s equator in the Southern Hemisphere and that they only graze the Northern Hemisphere. 1. What season do you think it is in the Northern Hemisphere for: a) Earth A? b) Earth B? (c) 2020 SFSU. DO NOT DISTRIBUTE 7 The image below shows how these direct sun rays land on the Earth during the Summer and how the indirect rays land on the Earth during the Winter. Notice how the same amount of rays land on the Earth in both Summer and Winter, but during the Summer the rays land in a smaller area then in the Winter. Figure 3: source: https://physics.weber.edu/schroeder/ua/SunAndSeasons.html You can test this for yourself by using a flashlight (or phone flash light). Point the light directly at a table (perpendicular) to represent Summer, then point the light at an angle (45◦ ) to represent Winter. You can also test this by using a small space heater. If you point the heater directly at yourself you may notice how much hotter it feels than if it were pointed next to you. 2. Do you think the patch of light on the table looks brighter or fainter in the winter or summer? 3. Do you think the Earth gets more energy in the summer or in the winter? Explain your reasoning. 4. Do you think that the effect of the Earth’s tilt on the intensity of the Sun’s rays can help to explain the seasons? Justify your answer. (c) 2020 SFSU. DO NOT DISTRIBUTE 8 Summary Questions: 1. Which of the four hypotheses listed at the beginning of the exercise were you able to rule out as plausible causes of the seasons, and why? (Include all that were ruled out.) 2. Which of the four hypotheses did you find could help to account for the seasons? More than one may be important; discuss the role played by each one. For Fun: Here is a short Bill Nye video explaining the seasons: https://youtu.be/ KUU7IyfR34o