Earth, Sun, and Seasons

In your map of the Solar System from the last activity, you should see that the asteroids form a circle in the sky above the Earth. That circle should remind you of the models of the Solar System that you might remember from your textbook: the planets and asteroids go around the Sun in invisible paths called orbits.

But why are the asteroid orbits tilted?

Explore 1. Explore the question of why the asteroid orbits are tilted. Look at the line you drew at Dec = 0 in the last activity. As you learned earlier, Dec = 0 corresponds to standing on the Earth’s equator and looking directly up.

Use a protractor to measure the angle between the horizontal line of Dec = 0 and the asteroids. What is the angle?

Tell your teacher what the angle was. He or she will record the angles from the entire class, and will tell you the average.

Most asteroids go around the Sun in a plane called the ecliptic. If you look back at the map of the planets that you made in the last activity, you will see that the planets move in the ecliptic too. The angle you measured in Explore 1 is the angle between the plane of the Earth’s equator and the ecliptic. This means that from the Earth’s perspective, the ecliptic is tilted. But from the Sun’s perspective, the ecliptic is straight and the Earth’s equator is tilted.