2. SUN & SEASONS

3. UFO Size of Stuff in the Sky Earth  * Eye/brain gauges angular size soccer ball  alone doesn’t give you true size!

4. Moon & Sun Earth   = 0.5 o Ack! [Pinky test.]

5. Angular Size & Distance Earth   = 0.5 o  > >  d

6. SOLAR MOTIONS

7. APPARENT MOTION OF SUN (Viewed from Earth) Diurnal (Daily) Motion: East to West, relative to horizon; rises & sets Annual Motion: Eastward relative to stars - reflection of orbit of Earth about sun - apparent path: Ecliptic

8. Meridian

9. Earth’s Orbit 1 2 Viewed from Earth, Sun circles sky once per year. 1 2

10. Sun appears to pass through 13 constellations: ‘Zodiac’ Gemini Cancer Leo etc... Ophiuchus

11. EQUINOXES & SOLSTICES

12. Vernal Equinox Autumnal Equinox Winter & Summer Solstices

13. Vernal Equinox: March 21 Autumnal Equinox: September 23 Summer Solstice: June 21 Winter Solstice: Dec 21

14. DAILY SOLAR MOTION CHANGES WITH SEASONS

15. Motion N/S of Celestial Equator  > Rising/setting points vary > Noon altitude varies > Duration of daylight varies Mar 21 – Sep 23: sun north of celestial equator  sun above horizon > 12 hrs Sep 23 – Mar 21: sun south of celestial equator  sun above horizon < 12 hrs Sep 23 & Mar 21: sun on celestial equator  sun above/below horizon 12 hrs

16. 41 o Mar 21 Sep 23

17. 41 o Mar 21 Sep 23 90 o – 41 o 23.5 o [State College]

18. Annual variation in motion of sun in sky results from... change in orientation of Earth relative to sun:

19. Summer Solstice Winter Solstice p. 24

20. Northern Winter Solstice

21. Northern Summer Solstice [Demo, #3]

22. REASONS FOR THE SEASONS

23. Temperature varies from season-to-season – Why? - Sunlight more direct in summer (than in winter) - More daylight hours in summer (and fewer in winter)

24. Northern Winter Solstice

25. Northern Summer Solstice

26. Summer SunWinter Sun

27. No significant temperature change due to change in Earth-sun distance - e.g., N. hemisphere not much closer to sun than S. hemisphere in summer - Earth actually closest to sun in January!

28.  January July  Earth’s Orbit – Exaggerated Earth only ~ 3% closer in January than July