1. The Night Sky

3. The celestial poles and equator
north celestial pole – point in the sky directly above the Earth’s north pole
south celestial pole – point in sky directly above the Earth’s south pole.
celestial equator – midway between the celestial poles (90 degrees away), lies directly above the Earth’s equator.

7. North celestial pole

8. South celestial pole

9. Star trails on the celestial equator

11. Discussion
This there any place on Earth where all the visible stars are circumpolar, never falling below the horizon? Explain.

12. Discussion
Is there any place on Earth where none of the visible stars are circumpolar? Explain.

13. Discussion
If we were at the North pole, how far above the horizon would the North celestial pole be?

14. Discussion
How high above the north horizon is the north celestial pole from Earth’s equator?

16. Discussion
How high above the northern horizon would the north celestial pole appear in Cleveland which has a latitude of about 42 degrees?

17. What is the latitude of this picture?

18. The constellations
Traditionally, a constellation is a grouping of stars in the same part of the sky.

19. Orion

21. The constellations
In modern astronomy, the constellations are 88 irregular areas that completely cover the sky. Thus, every celestial object lies within the boundaries of a constellation.

23. Ursa Major

26. Discussion
Why do you think ancient astronomers invented the constellations and made up stories to go with them?

27. Canis Major

28. Stellarium
Free planetarium software

29. Annual motion of the stars
The same stars are not visible all year long. Any given non-circumpolar star will set 4 minutes early each day until it becomes lost in the glare of the setting Sun.
This motion is caused by Earth’s yearly motion around the Sun.

30. In other words
While the Sun takes 24 hours on average to traverse the sky, the stars take only 23 hours and 56 minutes.
The Sun moves 4 minutes eastward each day relative to the stars.
Thus different stars are visible at different times of the year.

31. Solar and sidereal days
Solar day – 24 hours
Sidereal day – 23 hours 56 minutes is the actual rotation period of the Earth

33. The ecliptic
The ecliptic is the annual path through the sky that the Sun appears to take.
In other words, the ecliptic is the plane of Earth’s orbit projected onto the stars.

35. Constellations of the Zodiac
The ecliptic passes through 12 constellations (actually 13) during the year. This are know as the zodiacal constellations.