Sunlight and Seasons Part 1

Let’s look at the implications of the Greek’s Celestial Sphere model for sunlight on a non-moving, fixed Earth. In this model the Sun is fixed to the transparent Solar Sphere whose axis is pinned inside the Celestial Sphere and tilted at 23.5o from the North Celestial Pole. (See the graphic I handed out in class today.) Imagine that both spheres are centered on the Earth but are much larger than the earth. The Celestial Sphere rotates clockwise once on its axis every 23 h and 56 minutes, carrying the Solar Sphere with it. The Solar Sphere rotates about 1o (4 minutes) counter-clockwise each day. The combination of these two rotations means that it takes 24 hours for the Sun to return to the same point in the sky! Let’s begin by looking at the Earth…

Questions:1. How much of the Earth’s surface is illuminated by the Sun at any moment?

2. What does your answer to the last question imply about the distance from the Earth to the Sun?

For the questions that follow, the terms summer and winter refer to seasons in the northern hemisphere.

Equator

North Pole

HW #3

Name_____________________________ Per __

Study Buddy? ____________________________

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3. Sketch the apparent motion of the miniature Sun around the fixed Earth for one 24 hour period on the Summer Solstice. This is the view that someone would have if they could see the Celestial Sphere model from the outside! Start by drawing the Celestial Sphere with the Sun pinned to it. Then draw the path of the Sun as the Celestial Sphere rotates in 24 hours.

4. Now sketch the apparent motion of the miniature Sun around the fixed Earth for one 24 hour period on the Winter Solstice. Use the same approach you used in problem 3!

Note: Not to scale. The Sun is much farther away from the Earth, and is much larger than the Earth.

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