Earth-Sun Relationships The Earth is a relatively closed system; there are virtually no major inputs or outputs to the four Earth spheres that comprise our planet (the lithosphere, biosphere, atmosphere, and hydrosphere). The exception, of course, is the input and output of energy to the system. The Earth's primary source of energy is the sun.
Let's look at the relationship between the Earth and the Sun as we know it today. Like much about the Earth's history, this relationship has changed slightly over time as the Earth's orbit and tilt have changed (more about that later). But fundamentally, the general revolution of the Earth around the Sun has not changed since the formation of the universe, and this revolution is what determines our seasons.
Click on the button below and log in to the textbook website. If you have not previously done this, follow the instructions here. In the Study Area, select Interactive Animations, and click on the Earth-Sun relationships animation for Chapter 1. Use the animation to answer the following questions.
1. What day of the year does the Sun rise at the North Pole?
2. What latitude receives exactly 12 hours of daylight every single day of the year?
3. When the Northern Hemisphere is tilted towards the Sun, does Idaho receive more or less direct solar energy than when the Northern Hemisphere is tilted away from the Sun?
4. Currently, there are only two days of the year when the Earth's axial tilt is 0 degrees relative to the location of the Sun: the March equinox and the September equinox. Now, imagine that the Earth's axial tilt was 0 degrees in the orbital plane, instead of its current 23.5 degrees. How many hours of daylight would Idaho receive on December 21st? On June 21st? (Hint: look at the length of day portion of the animation and imagine the Earth's tilt being 0 degrees all year long).
5. If the axial tilt of the Earth was 0 degrees, would the amount of solar energy received in Idaho change at all over the course of the year?
6. If the axial tilt was 0 degrees, would Idaho have seasons?
7. Now, imagine that the axial tilt of the Earth is 33.5 degrees instead of 23.5 degrees. At what latitude would you find the Tropic of Cancer?
8. As the Sun's rays become more vertical for a given location, does that location receive more solar energy or less solar energy? (Hint: think about the difference during the summer -- when the Sun is higher in the sky -- as compared to the winter -- when the Sun is lower in the sky -- in Idaho)
9. Moscow, Idaho is at approximately 47 degrees N latitude. If the Earth's axial tilt was 43.5 degrees instead of its current 23.5 degrees, do you think that Idaho would have hotter or cooler summers? (Hint: think about places where the Sun is directly overhead like the equator on the equinoxes. What are the temperatures like there?)