The winter and summer solstices occur as a result of the Earth’s tilt. The summer solstice occurs for a hemisphere when it is facing most directly towards the sun, and this marks the longest time of sunlight for that hemisphere. The winter solstice, is the exact opposite occurrence, resulting in the least amount of time of sunlight in a day. The equinoxes, however, occur when the axis is not tilted towards or away from the sun, and thus no hemisphere gets any more light than the other. This also results in there being an even amount of light and dark on the equinoxes.
The most fascinating aspects about the equinoxes (and solstices too, although I don’t talk about it) to me is their significance that we can see they had on civilizations throughout history. Despite lacking the technology that we have, many early civilizations knew what equinoxes were, and when they would occur. This has resulted in some amazing monuments and mysteries left over into our age. The famous Mayan pyramid in Chichen Itza, Mexico was constructed to cast a serpent shadow on the equinox. Of course, another famous site is Stonehenge. This mystery, although little is known about its history, can be used to predict both equinoxes and solstices. Other examples from ancient civilizations around the world showed that many early people knew about and understood equinoxes and solstices. These are just some of the first steps in our history of attempting to understand the world around us. This ability to understand something far beyond the technological capabilities of the day is yet another example of why we as the human race continue to push the limits of our knowledge and explore the universe in which we live.