1. Nearby Constellations

2. (2-D “Constellations”, from Stars in 3-D !)

3. This several-hour-long time exposure, taken from tropical northern Australia, shows the clockwise motion of the southern stars around the South Celestial Pole. (Photo by David Miller/DMI.)David Miller/DMI Half-hour time exposure facing north & west. The stars are tracing counter-clockwise circles, centered on a point near the prominent North Star (Polaris). Notice the Big Dipper at the lower-left. “Circumpolar” Stars/Constellations

4. Earth shown at the center of the imaginary “Celestial Sphere”

5. Celestial coordinates: “Declination” (  ) and “Right Ascension” (R.A.) (=> “latitude” & “longitude”!)

6. The Sun’s apparent path through the Celestial Sphere... (actually due to Earth’s annual orbit about the Sun!)

7. “Summer Constellations” vs. “Winter Constellations”, due to Earth’s annual revolution about the Sun:

8. Earth, Sun, and the “Zodiac Constellations” through the Seasons “Summer Signs” = “Winter Constellations”; “Winter Signs” = “Summer Constellations”

9. An Earth-bound Observer sees only half the sky at any one time!

10. “Time Zones” (artificial!), & some famous Meridians around the globe:

11. “Northern” vs. “Southern” Celestial Hemispheres (& Northern/Southern Constellations!) (In Northern Winter/ Southern Summer…) =>

12. What causes the Seasons?

13. Seasonal observations Above is for a Northern Hemisphere location (“Summer” = Higher Sun and Longer Daytimes!)

14. “Land of the Midnight Sun”? (Or the Noon Darkness…?)

15. A good view from Stonehenge! (Sunrise on the Summer Solstice)

16. Ancient “Observatories” in the Americas! (Serving as “Calendars” & “Almanacs”…)

17. The Sun’s apparent path through the Celestial Sphere goes along the “Ecliptic Plane”… TILTED by ~23.5  with respect to Earth’s Rotation (NP/SP) Axis!

18. More Tilt with respect to the Sun => Stronger Seasons!

19. 1 Year  365.2425 Days  365.25 Days Christopher Clavius Pope Gregory XIII The lunar crater Clavius, with peripheral craters (Need “Leap Day” Corrections!)

20. “Solar Days” (= a day “by the Sun”) (= 24 hrs.) vs. “Sidereal Days” (= a day “by the Stars”) (= 23 hrs., 56 min.) => 1 Year  365.25 Solar Days  366.25 Sidereal Days

21. “Precession” of Earth’s Axis, and the temporary nature of the “North Star”...... and the “Vernal Equinox”!