Celestial Sphere Notes

1. Celestial Sphere Notes

2. Altazimuth Coordinate • Altitude • Degrees above the horizon • 0° to 90° • Azimuth • Degrees right of North • 0° to 360°

3. Altazimuth Coordinate • Horizon • Zenith • Meridian

4. Coordinate System

5. Celestial Sphere • Extension of our globe • North/South Pole • Equator

6. Celestial Coordinate • Latitude • Declination • Degrees above or below the equator • Longitude • Right Ascension • Hours to the right of north

7. Both

8. Real and Apparent Motion

9. Apparent Annual Motion • Caused by the Earth revolving around the Sun • Causes Sun to shift position against the stars by about one degree per day (360/365).

10. Apparent Diurnal Motion • Caused by the rotation of the earth • Causes everything in the sky to rise in the east and set in the west • Video

11. Length of Day • Sidereal (Stars) • 23hr:56min • Relative to the stars • The correct one • Synodic (solar) • 24hr • Relative to the sun • The one we use

12. Length of Month • Sidereal (Stars) Synodic (Solar) • 27.3 d 29.5 d • Relative to the stars Relative to the sun

13. Length of Year • Defined as when the Sun on the ecliptic crosses the Celestial Equator.

14. Precession • The Earth wobbles like any other gyroscope • Period = 26,000 yrs • Therefore the position of the sun relative to the stars changes slightly every year.

15. Tropical Year • 365.24 days • Mean Solar Year • Sun at moment of spring to next crossing.

16. Julian Year • 365.25 days • The one we use • Also a Julian Day • Stared on 1/1/4713BC • Today’s Date

17. Sidereal Year • 365.26 days • Star at moment of spring to next crossing.