Diurnal Motion & Annual Motion
2 Major Motions
• Earth rotation about axis (24 hr
period – west to east)
• Earth orbit about Sun (365.26 days
(1 yr) period ® seasons
(Moon’s orbit - 27 days)
• Smaller effect due to precession
of Earth’s axis
all motions counter-clockwise
(viewed from
N.P.)
N.P.
23.5°
Stars are
very distant (Proxima Centauri 1.3 pc @ 4.3 lyrs)
“ Project”
stars onto spherical surface with Earth at center
Sun
appears to move through constellations
â
Celestial Sphere
ecliptic
moon’s orbit
equatorial
plane
5°
23.5°