General Astronomical Information

The Earth's daily rotation and its orbit around the Sun are responsible for all of the apparent motion of the Sun. It is actually the rotation of the Earth that causes day and night, and the apparent motion of the Sun. The 24-hour rotation of our planet on its axis gives the illusion that the Sun, the planets and the mantle of stars move around us, rising in the east, culminating overhead and setting in the west, each and every day. This is called diurnal, or daily, motion. It's easy to observe the effects of Earth's motion by simply observing a shadow (cast by the Sun) moving across any wall or surface. Within 10 minutes you'll see a noticeable change in the shadow, and can actually watch it move almost imperceptibly across the surface. The speed of this shadow is the actual speed of the Earth rotating on its axis -- approximately one Zodiac degree every four minutes. The yearly orbit of the Earth around the Sun is the reason that the seasons and the stars change from month to month. As the Earth moves along in its orbit, the night side of the Earth faces outward to a slightly different part of the universe each night, moving about a degree a day (although in actual experience, it takes about a month for observable changes to occur). These changes are very regular, reflecting the routine and predictable nature of our orbit.