1. The Reason for the Seasons SESAME Astronomy Week 1 - January 12th, 2010

2. the year takes 1 day for earth to make 1 rotation (to rotate once) on its axis takes 1 year for earth to make 1 complete orbit (revolution) rotation axis tilted with respect to orbit rotation axis tilted in the same direction with respect to the background stars, no matter where in orbit earth is Huh?

4. direct vs. indirect light

11. Summer solstice - June 21st longest day of year sun as high as it gets in the sky Earth tilted toward sun Winter solstice - December 21st shortest day of the year sun as low as it gets in the sky Earth tilted away from sun Equinoxes - March 21st/September 21st equal number of hours of light and dark elevation of sun at noon equal to latitude Earth tilted neither toward or away from sun

12. So why is the winter solstice near the beginning of winter, and not the middle of winter?

13. There’s A LOT of water! Water takes a long time to cool off As the water cools off, it warms up the air (so air stays warm longer than sunlight can account for) Water takes a long time to heat up As the water heats up, it cools off the air (so air stays cool longer than sunlight can account for) After summer solsticeAfter winter solstice

14. Activities Play with computer demos Do sunrise/sunset activity Come back for summation and discussion of homework and projects

15. Summary Earth rotates on an axis once per day This axis is tilted with respect to Earth’s orbit around the sun When the Earth is tilted toward the sun, sunlight is “direct” (meaning: more concentrated) This concentrated sunlight heats up the part of Earth tilted toward the sun

16. Summary As the Earth moves around its orbit, the tilt faces away from the sun When the Earth is tilted away from the sun, sunlight is “indirect” (meaning: watered down) This watered down sunlight can’t keep the Earth warm, and the part of Earth tilted away from the sun cools off

17. Summary June 21st: summer solstice - most sunlight June 22nd: Earth moves away from summer solstice July-August: Earth still moving away from summer solstice, but water cools off and warms up air at same time to keep Earth warm through summer December 21st: winter solstice - least sunlight December 22nd: Earth moves away from winter solstice January-February: Earth still moving toward summer solstice, but water warms up and cools air at the same time to keep Earth cool through winter

18. Assignments Read through http://www.astronomy.org/programs/seasons/ http://www.astronomy.org/programs/seasons/ This website gives 2 common misconceptions about why we have seasons. For each misconception, imagine that one your students made that claim. Write what your response to the student would be. Please type your assignments. (You may draw diagrams, though.) Finish worksheets started in class Start sun project and moon project - have ready for project checks next Wednesday

19. Resources http://www.astronomy.org/programs/seasons/