Unit 5: Exploring the Nature of Astronomical Phenomena in the Context of the Sun
Unit 5: Exploring the Nature of Astronomical Phenomena in the Context of the Sun/Earth/Moon System
VIII. Using Central Ideas Based on Evidence to Develop an Explanatory Model for the Earth’s Seasons
A. Explaining the Earth’s seasons with a heliocentric model
Question 5.37 Why is it hot in the summer and cold in the winter?
An additional aspect of this heliocentric model is to envision the Earth as tilted on its axis. The tilt of the Earth’s axis of rotation has profound implications for variations in climate as the Earth revolves in its orbit around the Sun as shown in Fig. 5.69.
Note that the tilt is envisioned as always being in the same direction throughout the Earth’s annual trip around the Sun:
In the northern hemisphere, as shown in Fig. 5.69 for example, the Earth is envisioned as moving in a counter-clockwise direction around the Sun with the tilt is always in the same direction, toward the north star, Polaris. In spring, the tilt is toward Polaris but opposite to the counter-clockwise direction of motion around the Sun. In summer, the tilt is still toward Polaris and now toward the Sun but perpendicular to the counter-clockwise direction of motion. In autumn, the tilt is still toward Polaris but also in the counter-clockwise direction of motion around the Sun. In winter the tilt is still toward Polaris but away from the Sun, perpendicular to the counter-clockwise direction of motion.
To model the revolution of the tilted rotating Earth around the Sun :
- Which wall is in the north direction? east? south? west?
- Have someone hold the globe. Toward which wall should this person always tilt the axis of the globe?
- Which season is being represented by where this person is standing with respect to the lamp, the tilted globe, and the designated wall?
- Tilt backwards along the path around the lamp but toward the designated wall for spring
- Tilt both toward the designated wall and the lamp for summer
- Tilt forward along the path around the lamp and toward the designated wall for autumn
- Tilt away from the lamp but toward the designated wall for winter
- Have the person holding the globe keep the globe rotating on its axis and tilted toward the designated wall while walking around the lamp
- Where should the person be standing to represent:
- the spring equinox?
- the summer solstice?
- the autumn equinox?
- the winter solstice?
as the person walks around the lamp, while keeping the rotating globe’s axis tilted toward the designated wall?
Now everyone model the tilted rotating Earth revolving around the Sun:
- Tilt in the direction of the designated wall.
- Practice modeling the Earth’s daily rotation while tilted in this direction.
- Which season are you modeling?
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- Where are you with respect to the lamp and the constellations on the walls?
- Are you:
- tilted toward the designated wall but tilted backwards along the path around the lamp as you move forwards ? (spring)
- tilted toward both the designated wall and the lamp? (summer)
- til