poles and equator

At the icy North and South poles of earth, there is nearly no daylight at winter's peak. There are days when the sun does not quite ever make it over the horizon, and darkness reigns, peppered with stars and showy auroras. In summer, the sun is visible most of the day and night. At summer solstice, the sun never sets at all, but rides low, circling around the horizon.

The experience at the planet's equator is so very different. There is little change in the warm temperatures from one season to the next - you might say there are no seasons. All days are the same length throughout the year, as are the nights - and the days and nights are of equal duration. The sun rises and sets at the same location every day of the year, and it rides high across the sky.

If you live at a latitude exactly between one of the poles and the equator, you experience four seasons, and the lengths of the days and nights shift gradually from day to day. Days and nights of equal duration occur on the equinox. The longest day occurs at the summer solstice, the shortest at the winter solstice. The position of the sunrise and sunset shifts each day, reaching the farthest points at the solstices before gradually moving back to due east and west at the equinoxes.

The ancients of China, and the Americas, and Greece studied these events with great thoroughness through observation. Calendars came into existence using these observations to pinpoint the passing of a year and each season. The phases of the moon marked the months.