1. The Reason We Have Seasons By Chris Glass Math 341 December 1, 1999

2. Introduction In the following presentation I’m going to familiarize you the audience with the astronomical processes which produce our seasons.

3. Topics of Discussion n Within my presentation I’ll be discussing the following topics: n Obliquity n Tropics n Perihelion n Vernal Equinoxes or Solstices n Precession

4. Obliquity n Tilt of the Earth’s axis with respect to a direction perpendicular to its orbital plane n Occasionally varies by a few degrees but is currently valued at 23.4 degrees n In Summer Sun’s rays are much more concentrated (diagram) n Important to realize that the seasons are opposite in the Southern Hemisphere

5. Tropics n Points on the Earth’s surface where the Sun’s rays strike vertically n Tropic of Cancer and Capricorn located approximately 23 degrees north and south latitude of the equator n Occurs on Summer and Winter Solstices around December 22 and June 21

6. Perihelion n Point in the Earth’s orbit which is closest to the Sun n Currently occurs around the first of January n Regresses with time (one full day every 58 years) n Winter is now taking place when we are closest to the Sun

7. Vernal Equinoxes or Solstices n Two days of the year when Earth is tilted most toward or away from the Sun n Latter part of March and September n Predictors of day and night n Northern Hemisphere has longer days until September Equinox, and the date of equal day and night will occur before the March Equinox (diagram)

8. Precession n Change in the direction of the Earth’s axis n Caused by gravitational torque produced by the Sun and Moon (oblate and spinning) n Alters half degree every century n Effects on northern direction (Polaris) n Slight adjustments in seasonal patterns

9. The Future n Will be some definite impacts from these processes n More drastic effects for future generations n Space is an vast unknown which may lead us to new discoveries

10. Conclusion It’s truly amazing that the beauty we are blessed with year in and year out is a direct result of all these processes. The Seasons are magnificent creations which we should all treasure throughout our lives, and just an extra little bit of information my personal favorite is Fall.