WHY DO THE LENGTHS OF DAY AND NIGHT CHANGE WITH THE SEASON AND LATITUDE?

1. WHY DO THE LENGTHS OF DAY AND NIGHT CHANGE WITH THE SEASON AND LATITUDE?

2. September 21 VIEW FROM OVER THE SUN LOOKING DOWN ON EARTH’S NORTH POLE. North Pole (Constant tilt) SUN December21 June 21 N 66.5°N March 21 Arctic C. Cancer 23.5°N Equator 0° Capricorn 23.5°S Antarctic C. 66.5°S s

3. VIEW FROM OVER THE SUN LOOKING DOWN ON EARTH’S NORTH POLE. September 21 North Pole (Constant tilt) SUN December21 June 21 Circle of Illumination Day/Night March 21 Half of Earth in darkness

4. September 21 SUN June 21 December21 March 21

5. SUN December21 June 21 N Arctic C. Cancer March & September 21 Equator Capricorn All places in the world spend equal lengths of time in the dark (night) and lighted (day). EQUINOXES Antarctic C. s

6. September 21 SUN December21 June 21 March 21 N Places in northern hemisphere spend more than half a day in darkness. Proportion of rotation in darkness increases to the Arctic Circle December21 Arctic Circle Places in southern hemisphere spend more than half a day in light. Proportion of rotation in daylight increases to the Antarctic Circle s Antarctic Circle

7. September 21 SUN December21 March 21 Places in northern hemisphere spend more than half a day in light. Proportion of rotation in daylight increases to the Arctic Circle. June 21 Arctic Circle N Places in southern hemisphere spend more than half a day in darkness. Proportion of rotation in darkness increases to the Antarctic Circle. Antarctic Circle s

8. September 21 SUN December21 June 21 N N s s N Arctic C. Cancer Equator Capricorn Antarctic C. s March & September 21

9. N N N Arctic C. Cancer Equator Capricorn Antarctic C. s s s

10. THE BOTTOM LINE

11. THE BOTTOM LINE • 1. All places at the equator receive 12hrs of daylight and 12hrs of darkness regardless of the season.

12. N N N Arctic C. Cancer Equator Capricorn Antarctic C. s s s

13. THE BOTTOM LINE • 1. All places at the equator receive 12hrs of daylight and 12hrs of darkness regardless of the season. • 2. On March 21 and September 21 (Equinoxes) all places in the world receive 12 hrs of daylight and 12hrs of darkness regardless of their latitude.

14. N N N Arctic C. Cancer Equator Capricorn Antarctic C. s s s

15. THE BOTTOM LINE • 1. All places at the equator receive 12hrs of daylight and 12hrs of darkness regardless of the season. • 2. On March 21 and September 21 (Equinoxes) all places in the world receive 12 hrs of daylight and 12hrs of darkness regardless of their latitude. • 3. All places lying north of the Arctic Circle (66.5°N) or south of the Antarctic Circle (66.5°S) will experience at least one day of total darkness and one of total daylight.

16. N N N Arctic C. Cancer Equator Capricorn Antarctic C. s s s

17. THE BOTTOM LINE • 1. All places at the equator receive 12hrs of daylight and 12hrs of darkness regardless of the season. • 2. On March 21 and September 21 (Equinoxes) all places in the world receive 12 hrs of daylight and 12hrs of darkness regardless of their latitude. • 3. All places lying north of the Arctic Circle (66.5°N) or south of the Antarctic Circle (66.5°S) will experience at least one day of total darkness and one of total daylight. • 4. As one moves geographic position from the equator to the poles the differences in summer and winter lengths of day and night become more extreme.

18. Spitzbergen, Norway, Midnight, June 21. Fairbanks, Alaska, Midday, December 21.