AS101 Lecture Notes - Lecture 2: Orbital Mechanics, Apparent Retrograde Motion, Ecliptic
The location of the sun in the sky depends on the time of day, the time of year and your location on the face of the earth. The north-south axis (its rotational axis) is not perpendicular to the ecliptic plane; rather, it is tipped at 23. 4 to this plane. The moon"s orbit is not precisely circular, its distance from earth varying from about. The orbital period (from one full moon to the next) is almost exactly 29. 5 days. However, its sidereal period, the time for one revolution relative to the stars, is a little over 27 days. the moon spends most of its time either above or below the ecliptic plane. Only when it is crossing through this plane, at points called nodes, is an eclipse possible. During this entire eclipse cycle the shadow of the moon is racing across the surface of the. Earth at a speed of around 1600 km/hr.