1. Solar vs. Sidereal Day

2. An Earth Day
Sidereal Day: 23 hr 56 min 4 sec Motion relative to background stars
Mean Solar Day: 24 hours The average time between meridian crossings of the Sun
Apparent Solar Day: varies The actual time between the meridian crossings

4. Earth Orbits Sun

5. The Ecliptic

6. Tilt of Spin Axis

7. Ecliptic: Path of the Sun

8. The Equinoxes and Solstices
Tilt of the spin axis is related to the seasons
Effect of tilt on climate is not instantaneous

9. Ecliptic on the Celestial Sphere

10. An Earth Year
Based on the motion of the Sun on the sky or the motion of Earth around the Sun
Julian Year: mean solar days. Used in calendars before 1582.
Gregorian Year: mean solar days. Used in calendars today.

11. An Earth Year
Sidereal Year: mean solar days. Defined by the motion relative to stars.
Anomalistic Year: mean solar days. Defined as perihelion to perihelion.
Tropical year: mean solar days. Defined from equinox to equinox. Thus, related to the seasons.

12. Sun Changes Declination

13. The Arctic and Tropical Regions
How are the arctic and tropical regions defined?
Can you answer this without looking at your books?
Have you ever been to these regions?

14. Back to the North Pole

15. Cold Arctic Regions

16. Land of the Midnight Sun

17. Back to the Equator

18. Tropical Heat In the Tropics, Sun is always close to zenith
In the Tropics, the sun reaches the Zenith at some point in the year
Lots of heating due to sunlight