Cycles Of The Sky

Introduction We are all familiar with at least one important cycle of the sky: the cycle of day and night. The sky appears to rotate from east to west, bringing with it the rising sun and, after sunset, the stars. This apparent rotation of the sky is caused by the rotation of the earth.

There are many other cycles of the sky. The next most obvious, perhaps, is the monthly cycle of the moon's phases. Less obvious, but much more important to our well being, is the gradual motion of the sun eastwards during the course of the year, due to the counterclockwise revolution of the earth around the sun (as seen from the north celestial pole).

Topics

Annual motion of the Sun

The ecliptic

The equinoxes

	spring (vernal)
	autumn (autumnal)

The solstices

	summer
	winter

The seasons

Lunar Cycles

	phases
	sidereal period (27.32 days)
	synodic period (29.53 days)

Tides

Eclipses

	Lunar
	Solar
	1998

Last updated August 26, 1998 Harrison B. Prosper