Even though we aren’t physically aware of it, the Earth is in a constant state of rotation and revolution. Our only indications are the very obvious differences in day and night, and the changing of the seasons caused by this never ending movement. Every twenty four hours, the Earth rotates on its axis, bringing our particular location either sunlight or darkness. However, every 365 days, more or less, the Earth also revolves around the sun. As the Earth revolves around the sun, it is tilted, so that the side tilted toward the sun receives the most sunlight, and the side tilted away, receives the least. This accounts for the fact that when it is summer in one hemisphere, it is winter in the other.
March 20th or 21st, and September 22nd or 23rd, mark events known as an equinox, when the Earth’s axis is not tilted. On these days, known as either the vernal or autumnal equinox, the equator is on the same plane as the Earth’s equator, and the period of daylight hours and night are equally divided. After the spring, or vernal equinox, the sun continues to climb higher and higher into the sky until it reaches its peak during the summer solstice. During the period after the autumnal equinox, the reverse is true. The dates of the vernal and autumnal equinox are considered to be the first days of spring and fall, and mark the beginning of either warmer or colder days ahead.
Two other days, known to be very important to the ancients, are the solstices. Around June 21st, and December 21st. During the summer solstice, the sun reaches its highest point at noon, and during the winter solstice, its lowest. This produces the longest and shortest days of the year, and mark the beginning of summer and winter.
The change in the seasons, and the overall temperature variations around the globe are related directly to the tilt of the Earth. This is the reason that the poles are colder, and the equator, which benefits from more direct sunlight is hot. In fact, since the Earth is tilted, the poles are never directly pointed toward the sun. Temperature changes between summer and winter are the result of two major factors, the angle of the sun’s rays, and the length of time that the sunlight is available. In the summer the angle is more direct, the rays are less spread out and consequently, more concentrated. The days are also longer, giving the area more time to accumulate heat. In the winter, of course, the opposite is true. The angle is less direct, and the days are shorter.