1. Sky Motions
Diurnal Motion
Annual Motion

2. DIURNAL MOTION Daily East / West motion of the sky
Due to the Earth’s rotation (15°/hour)
[360°/24 hours = 15°/hour]
[1° in 4 minutes]
Stars fall into two groups
Circumpolar - never rise or set
Equatorial

3. Circumpolar Stars

4. Equatorial Stars

5. View from the North Pole

6. View from the Equator

7. Coordinate System

8. Celestial Meridian
Circle going through north and south points on the horizon and the zenith Z

9. Celestial Meridian
Objects on the Meridian are at their highest point in the sky (transit)
Astronomical noon is when Sun is on the Meridian.
Does not mean the Sun is directly overhead.
Midnight is when the Sun is on the Meridian below the horizon.

10. Annual Motion

11. Horizon Calendar

12. Sunrises and Sunsets The Sky Dome Polaris W S N E
On the day of an summer solstice… W
On the day of an winter solstice… S
On the day of an equinox… N E

13. Starting Points for the Sun
Polaris W
Vernal or
Autumnal
Equinox S
Winter
Solstice
Summer
Solstice N E
Starting Points for the Sun

14. Sunrise in Athens

15. Stonehenge

16. Earth’s Annual Motion
Leo

17. NCP Celestial Sphere Ecliptic Celestial Equator SCP Autumnal Equinox
23.5°
Vernal Equinox

18. Sun’s Motion Tool

19. Inclined Pole causes Seasons
Northern Hemisphere Summer N S
23.5°
Northern Hemisphere Winter

20. Sun’s motion along the Ecliptic

21. ANNUAL MOTION Constellations move westward during the year.
Due to Earth’s orbital motion around the Sun
Sun appears to moves eastward 1°/day
Path of the Sun called the ECLIPTIC
Ecliptic inclined 23.5° to Equator
Horizon calendar

22. Annual Motion Affects the Nighttime Sky
Day 1
9:00 PM

23. Annual Motion Affects the Nighttime Sky
Day 2
8:56 PM

24. Annual Motion Affects the Nighttime Sky
8:52 PM
Day 3

25. Annual Motion Affects the Nighttime Sky
9:00 PM
One Year Later

26. “Stars” Fixed Stars Planets - traveling or wandering stars
Modern concept of stars
Form the Constellations
Planets - traveling or wandering stars
Sun, Moon, Mercury, Venus, Mars, Jupiter, and Saturn
Meteors - “shooting stars”
Comets - “long-haired stars”

27. Babylonian Astronomy

28. Babylonian Astronomy
Star Charts

29. Babylonian Astronomy Fatalistic Pre-determinism
Everything in nature pre-determined by the gods
Doesn’t lend itself to model building
Infinite time line

30. End of Section