2. LEARNING GOALS I will discuss seasonal variation in day length as a consequence of axis tilt, rotation, and revolution.

3. Seasons and Sun

5. MOVIE: Reasons for the Seasons Reasons for the Seasons Reasons for the Seasons

6. SUNSHINE I’ve heard it said that December 21 is the shortest day of the year. Why would someone say that? Do we have fewer than 24 hours on December 21? We get fewer hours of sunlight in winter, more hours of sunlight in summer, but the sum of light and dark hours always equals 24.

7. SUNSHINE If it is true that there is a shortest day, is there also a longest day of the year? June 21

8. SUNSHINE How many hours of sunlight will we have today? Sunrise= 7:15am Sunset= 6:12pm Calculate the hours and minutes. –Hint: Calculate the hours and minutes between sunrise and noon, then between noon and sunset, then add them together.

9. SUNSHINE Example: –Sunrise=7:15am –Sunset=6:12pm 7:15-11:15= 4 hours 11:15-12:00= 45 minutes –So 4 hours,45 minutes 12:00-6:00= 6 hours 6:00-6:12= 12 minutes –So 6 hours, 12 minutes Total= 10 hours, 57 minutes

11. GRAPH QUESTIONS What does the graph reveal about the amount of daylight over a year in Berkley? –Days get longer from January to June, shorter from June to December When do people in Berkley have their longest day? Shortest? –Longest= June, Shortest= December When do people in Berkley have about 12 hours of daylight? –March and September

12. GRAPH QUESTIONS How many hours of daylight do people in Berkley have on their longest day? On their shortest day? –Longest= 14+, Shortest= 9+ In what season do people in Berkley have their longest day? Their shortest day? –Longest= Summer, Shortest= Winter

13. GLOBAL DAYLIGHT When one location on Earth has 14 hours of daylight, is all the rest of the world having 14 hours of daylight as well? Is the longest day of the year the same length all over the world? Is the longest day of the year the same day all over the world? Are the longest days always in the summer? Are the shortest days always in the winter?

14. READING: “Wendy and Her Worldwide Weather Watchers” page 12