Topic 2: Naked Eye Astronomy Reading: Chaisson & McMillan, Ch. 1 Local Sky Maps Your Sky

1. Celestial Sphere

2. Rotation of the Earth on its axis:

• Daily Motions (diurnal motions)

3. Revolution of the Moon about the Earth:

• Monthly variations
• eclipses
• tides

4. Revolution of the Earth about the Sun:

• Annual variations

5. Motions of the planets

6. Important Celestial Periods

Motion	Period	Comments
Sidereal Day	23 h 56 m 04 s	day according to the stars
Solar Day	>23 h 56 m 04 s	day according to the Sun
Mean Solar Day	24 h 00 m 00 s	average Solar day
Sidereal Month	27 d 07 h 43 m 11 s	Moon month with respect to the stars
Synodic Month	29 d 12 h 44 m 03 s	length of the lunar phase cycle
Sidereal Year	365 d 06 h 09 m 10 s	year with respect to the background stars
Tropical Year	365 d 05 h 48 m 46 s	year of the seasons
Precession	~25,800 y	slow rotation axis movement

7. Calendars through the Ages