1. The ReasonS for the Seasons Lesson 4

2. In which direction does Earth’s axis point as it revolves around the Sun?

3. In which direction does Earth revolve around the Sun?

4. This diagram is greatly over exaggerated Perihelion (Closest)=147,098,291 km Aphelion (Furthest)=152,098,233 km

5. The relative to scale size of the Earth’s elliptical (oval shaped) orbit: (Would you have called it a circle?)

6. Perihelion (closest to the Sun) January 4 th Aphelion (farthest from the Sun) July 4 th So why do we have such a strong misconception about the cause of the seasons? January 4th July 4th

7. The Angle of the Sun’s Solar Radiation

8. This data is pretty close for our location: (Seattle is close to 47°N latitude) Summer – 16 hrs of daylight, angle of sun 63°, average high temp 71°F Fall – 12 hrs day, angle 40°, high temp 67°F Winter – 8 hrs day, angle 16°, high temp 47°F Spring – 12 hrs day, angle 40°, high temp 58°F

9. Big Ideas: Yes it is true that the seasons are caused by the tilt of the earth, but... The tilt of the earth determines how much solar radiation (sun’s energy) we receive. When we are tilted toward the sun (summer solstice) we not only receive more solar radiation, but we are being hit by a more direct angle increasing the intensity of the solar radiation. (Con’t)

10. Big Ideas (Continued) During our winter solstice (Dec. 21 st ) we are receiving less solar energy and the solar energy is hitting us at a less direct angle so the energy is spread out more and as a result weaker. Solstice - longest/shortest day of the year. Equinox - equal day and night world wide. (Continued)

11. Big Ideas (Continued) March 21 st Spring (Vernal) Equinox (NH) June 21 st Summer Solstice (NH) Sept. 21 st Fall (Autumnal) Equinox (NH) Dec. 21 st Winter Solstice (NH) NH = Northern Hemisphere. The seasons are reversed for the Southern Hemisphere.