It’s summer solstice time for us in the Northern Hemisphere. This solstice occurs at the instant the sun reaches its most northerly point on the celestial sphere, the imaginary sphere of stars surrounding Earth. If you stood inside the Stonehenge monument on the day of the northern summer solstice, facing north-east through the entrance towards a rough hewn stone outside the circle – known as the Heel Stone – you would see the sun rise above the Heel Stone, as illustrated in the image below.
In 2014, summer solstice for the Northern Hemisphere (winter solstice for the Southern Hemisphere) will take place on June 21 at 10:51 Universal Time (5:51 a.m. CDT in the United States). That means that if you live in the western U.S., the exact time of this solstice happens before sunrise.
In the northern hemisphere at this time of year, the sun is shining on us most directly at midday. Except at high northerly latitudes, above the Arctic Circle – where daylight is continuous for many months – the day on which the summer solstice occurs is the day of the year with the longest period of daylight. Meanwhile, it is the shortest day for Earth’s Southern Hemisphere.
At the northern summer solstice – always around June 20 – the sun’s path stops moving northward in the sky. For us in the northern hemisphere, it’s the day on which the days stop growing longer and will soon begin to shorten again. For this reason, in festivals and celebrations across this hemisphere of Earth, the summer solstice is a time of celebration.
Stonehenge is tied to the winter solstice, too. At Stonehenge in England on the day of the northern winter solstice (always around December 20), people watch as the sun sets in the midst of three great stones – known as the Trilithon – consisting of two large vertical stones supporting a third, horizontal stone across the top.
In the case of Stonehenge, this great Trilithon faces outwards from the center of the monument, with its smooth flat face turned toward the midwinter sun. In fact, the primary axes of Stonehenge seems to have been carefully aligned on a sight-line pointing to the winter solstice sunset.
This Stonehenge monument – built in 3,000 to 2,000 BC – shows how carefully our ancestors watched the sun. Astronomical observations such as these surely controlled human activities such as the mating of animals, the sowing of crops and the metering of winter reserves between harvests. Stonehenge is perhaps the most famous of of the ancient astronomical monuments found around the world.