Seasons

1. Seasons Ch 22.2 Solar Energy and the Atmosphere page 555 Why do we have them?

2. The Orbit of the Earth • closest point to the Sun --perihelion: • distance is about 147 millions of km. • We are closest to the Sun in January. • farthest point to the Sun --aphelion: • the distance Sun-Earth is about 152 millions of km. • We are farthest from the Sun in July. • During the equinoxes, the distance Sun-Earth is about 149.5 millions of km.

3. So . . . distance is not the cause of the seasons So WHAT IS???

4. The earth has a 23.5° tilt! Know This • tilt of Earth and other planets originates from collisions with large bodies during the formation of the planets in the solar system

5. Solar Energy p 559 • The important thing is that the angle at which the sunlight hits the earth • See the two equal amounts of sunlight • The pink box receives the same total amount but it is spread out over a larger area • So it receives a smaller portion of the heat

6. Angle of Incidence

7. The Seasons • Because of the Earth's tilt, on June 21st, the sun is directly overhead on the tropic of Cancer in the northern hemisphere and on December 21st, the sun is directly overhead on the tropic of Capricorn in the southern hemisphere: • These are called solstices • In March and September 21st, the sun rays strike the equator most directly: the Earth is illuminated from pole to pole: this is the equinox.

8. Equator, Tropic of Cancer, Tropic of Capricorn, Arctic Circle

9. Equator • The tropic of Cancer • located 23.5° north of the Equator. • On June 21st, the sun is directly overhead the tropic of Cancer at noon • The tropic of Capricorn • located 23.5° south of the Equator. • On December 21st, the sun is directly overhead the tropic of Capricorn at noon • The Arctic Circle/Antarctic • located 23.5° south of the North Pole/North of South Pole

10. Terrestrial Radiation • The sun sends primarily short-wave radiation • This is absorbed by earth’s surface and reradiated as long wave IR rays • The lower atmosphere is mainly warmed by this terrestrial radiation

11. The Greenhouse Effect

12. Greenhouse gases • Carbon dioxide is one of the greenhouse gases. • carbon dioxide molecule can absorb infrared radiation and the molecule starts to vibrate. • Eventually, the vibrating molecule will emit the radiation again, and it will likely be absorbed by yet another greenhouse gas molecule. • This cycle serves to keep the heat near the surface, insulating the surface from the cold of space.

13. What would happen if the Earth's axis was not tilted? If the axis of the Earth was not tilted, the Earth would receive the same illumination all year long!

14. Try these multiple choice ?’s

15. The imaginary pole that runs through the center of Earth is called the _____. • axis • equator • South Pole • North Pole

16. The four seasons are a result of the tilt of Earth's axis and Earth's ___. • loss of internal heat • orbit around the sun • distance from the sun • rotation about its own axis

17. The northern hemisphere is tilted toward the sun during the month of _____. • January • April • July • October

18. When the northern hemisphere is in the middle of winter, the southern hemisphere is in the middle of ____. • spring • summer • fall • winter

19. Between December and June, the tilt of Earth's axis _____. • shifts by about 25 degrees • shifts by about 45 degrees • shifts unpredictably • does not change

20. Which of these is a major greenhouse gas? • CaCO3 • H2O • CO2 • NH3

21. The Atmosphere and Solar Radiation The atmosphere affects radiation in several ways • Upper atmosphere absorbs almost all radiation shorter than visible light • N2 and O2 in thermosphere and mesophere absorb the x-rays, gamma rays, and UV rays

23. Most of the rays that reach the lower atmosphere, like visible and infrared, have longer wavelengths • Most of the incoming infrared is absorbed by carbon dioxide

25. Does page 556 Fig 2 agree with this graphic?

26. Albedo-See page 557