1. Seasons What do your students think causes the seasons? http://nix.ksc.nasa.gov/info By the Lunar and Planetary Institute For use in teacher workshops

2. 10/4/2015The Seasons2 Rotation vs. Revolution Rotation is the spin of an object about its axis. –The Earth rotates once a day (once every 24 hours). Revolution is the orbit of one object around another. –The Earth revolves around the Sun every 365.26 days.

3. Solar Heating The sun or any light, heats a surface most effectively when it is shining directly onto the surface.

4. 10/4/2015The Seasons4 Day Night Cycle

5. True color images June December March September http://www.nasa.gov/vision/earth/features/blue_marble.html

6. What Causes Earth’s Seasons? Earth’s axis is tilted 23.5 degrees – it always points in the same direction (Polaris, the North Star) as we orbit our Sun once a year This tilt causes the hemispheres to alternate in the amount of our Sun’s light and heat they receive through the year http://www.lpi.usra.edu/education/skytellers/seasons/about.shtml

7. 10/4/2015The Seasons7

8. More daylight hours, more direct sunlight Northern Hemisphere Summer http://www.lpi.usra.edu/education/skytellers/seasons/about.shtml

12. Seasons vs. hemispheres Northern and southern hemisphere have reversed seasons.

13. Seasons In summer, the sun is at a smaller angle, more effective heating. In winter, the sun is at a larger angle, less effective heating.

14. 10/4/2015The Seasons14 Seasons Misconception Many people carry the misconception that the seasons are due to the distance of the Earth from the Sun. However, consider the following facts: –The Earth’s orbit around the Sun is nearly a perfect circle. The Earth is slightly closer to the Sun in January and farther from the Sun in July. Perihelion (closest to the Sun) is around January 3 when Earth is about 91,405,436 miles from the Sun. Aphelion (farthest from the Sun) is around July 4 when Earth is about 94,511,989 miles from the Sun.

15. 10/4/2015The Seasons15 Seasons Misconception –While it is winter in the Northern hemisphere it is summer in the Southern hemisphere. If the seasons were due to our distance from the Sun both hemispheres would have the same seasons at the same time.

16. Earth’s orbit is almost a perfect circle Earth is CLOSEST to our Sun (91 million miles) in winter—January 3 Earth is farthest from on our Sun (94 million miles) in summer –July 4

17. Equinox Sun rises due east Sun sets due west Exactly 12 hours of day, 12 hours of night Once in spring Once in fall When the sun is directly over the equator.

18. Solstice Summer solstice: Longest daylight off the year Sun at noon is highest in the sky Winter solstice: Shortest daylight off the year Sun at noon is lowest in the sky

19. Daylight Hours Across the Globe Time is indicated as number of hours (h) Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec 10.5 h 11 h 12 h 12.5 h 13 h 14 h 14.5 h 14 h 12.5 h 12.5 h 11 h 11.5 h 14.5 h 13.5 h 13.5 h 12.5 h 11 h 11 h 11 h 11.5 h 11.5 h 12.5 h 14 h 14.5 h 12 h 12 h 12 h 12 h 12 h 12 h 17.5 h 15.5 h 13.5 h 11.5 h 10 h 8.5 h 8.5 h 9.5 h 11.5 h 13 h 15 h 16.5 h 5 h 7 h 10 h 13.5 h 17.5 h 21.5 h 22 h 18 h 15.5 h 11.5 h 8.5 h 5.5 h 12 h 12 h 12 h 12 h 13 h 13 h 12 h 12 h 12 h 12 h 12 h 12 h 15 h 14 h 13.5 h 12.5 h 11.5 h 10 h 10.5 h 11 h 11.5 h 12.5 h 14 h 14 h 9 h 10 h 11 h 13.5 h 15 h 17 h 16.5 h 15.5 h 13.5 h 11.5 h 10.5 h 9.5 h 24 h 24 h 19 h 14.5 h 0 h 0 h 0 h 0 h 7 h 15 h 24 h 24 h Miami Brisbane Nairobi Punta Arenas Nome Singapore Cape Town Seattle Vostok http://www.lpi.usra.edu/education/skytellers/seasons/activities/light.shtml

20. Seasons Diagram The seasons are cyclical. They occur in order: Winter, Spring, Summer, Fall (Autumn).