When is the Summer Solstice? That time of the year when the Northern Hemisphere is angled toward the sun? When the day is the longest and when the night is the shortest? When the season changes into Summer? June 21st? Such astronomical knowledge is taught in grade school. However, observers in the Stone Age had no idea about the tilt of the Earth. They had no calendar or concept of hours, or even the ability to track the number of days or hours by simple arithmetic. All knowledge was passed down by story-telling. There was no mathematics. How did those who lived during the Stone Age figure out when the Summer Solstice occurred?
Knowledge of the solstices was crucial to nomadic Stone Age peoples. Seasonal changes bring drastic weather shifts in the Northern and Southern Hemispheres. Animals migrate. The ground is less fertile in the Winter months. Nomadic Stone Age tribes needed to know when to prepare to move or to stay. The sacred knowledge of the Winter and Summer Solstice was probably one of the first things passed down from shaman to shaman so they could guide the tribe.
To any solar observer, the sun rises in the east and sets in the west, but to a careful observer, the sun rises and sets in a little different place each time. If someone sat and watched the sunrise every day from the same place, they would notice the sun creeps along to the north or south, depending on the season, every morning. If it were Spring, they would notice the sun creeps slowly to the north every morning, until one day it would rise in the same place for a couple of days, then slowly creep back again toward the south. This stopping point on the horizon, the solstice, which means “when the sun stands still” in Latin, is the marker for the Summer Solstice. There is a similar point on the horizon for the Winter Solstice on December 21st, and another for the equinox, when night and day are the same length of time. At some point in the distant past, Stone Age observers figured this out, and began to be able to predict the seasons. Marking solar stopping points on the horizon was the first crude human calendar.
The Sun’s shift from north to south and back during its diurnal path is the result of the Earth’s angle of tilt from the ecliptical plane, known as the obliquity of the ecliptic. It should come as no surprise that the early awareness of these solar positions led the way to one of the first great accurate measurements of Astronomy by the Ionian Greeks. Around 450 BCE, Oenopidos of Chios measured the angle between the celestial equator and the ecliptic and came up with 24 degrees, a remarkably accurate measurement considering the actual angle was closer to 23.5 than it is today (23.44). He did not know he had discovered evidence of the axial tilt of the Earth, but nevertheless it was a signal moment in astronomical measurement. It led the Greeks to devise a calendar based on mathematics and not on crudely watching the horizon for Winter and Summer Solstice markers.
Many archaeologists believe that the Stone Age menhir complexes, circles of standing stones, that dot remote places in Northern Europe were solar and lunar observatories that aided in the observation of the Winter and Summer Solstice. It has been suggested often that Stonehenge was an ancient solar observatory, but despite hundreds of years trying to find a connection with the solar and lunar cycles, nothing definitive has been proven. From archaeological evidence of the menhir complexes, most scholars think Stonehenge and other similar sites were populated during the Winter Solstice, not the Summer. The druids of Stonehenge legend did not appear in Salisbury Plain until 5,000 years after the complex was built.
How long it took Stone Age peoples to figure out the Winter and Summer Solstice will probably never be known. When they finally did, however, it began the long quest to understand the stars that still continues today.
By Steve Killings