The Human Connection to the Sun
Keeping track of the Sun's cycles has always been important to human cultures. Seeing a certain star or constellation rise just before the Sun or set just after the Sun fixes a certain time of the year, and might tell the people of a culture that it is time to plant or to expect the river to flood. Since the very existence of a people may depend on these agricultural cycles, the Sun has played an extremely prominent role in early cultures around the world. It's pretty natural that the Sun God in many pantheons is the chief god, who grants life to the other gods and humans. In ancient Egyptian mythology the rising of the Sun each day was viewed as a literal reenactment of the creation. The Sun also figures large in human art. Solar figures representing renewal and life abound. It is no coincidence that Christian artists have traditionally portrayed God as radiating light (and glory).
Many ancient cultures established special places or "observatories" for tracking the seasonal motion of the Sun in the sky. The point on the horizon where the Sun appears to rise or set changes over the year. There are many archeological sites all over the world that are thought to provide views of special places on the horizon, such as notches between mountain ranges where the Sun appears to rise on the winter or summer solstices, important dates in the solar calendar.
Solstices and Equinoxes
The solstices are easier to observe than the equinoxes, since the Sun appears to stop rising further and further north on the summer solstice, stops, and begins moving south again day after day ("solstice" is derived from the Latin "sun stands"). Thus, keeping track of the rising of the Sun can also fix the time of year. When the days have been getting shorter and shorter and the Sun getting lower and lower it's very reassuring to know when the trend has stopped and the Sun is returning to "life". Celebrations of this moment (sometimes to ensure that it happens!) are common. It is important to note that "observatories" such as Stonehenge and Machu Picchu are about ceremony and not precision observations. That said, there are some structures, particularly in civilizations such as China, that allow quite accurate measurement of the length of the year.
Keeping track of daily and seasonal cycles is also important to humans for navigation. Watching the path of the Sun through the sky and observing its altitude at noon can help an observer determine latitude. Observations of the Sun combined with an accurate clock allow an observer to determine longitude.
