The summer solstice is almost here. This astronomical event not only marks the beginning of summer, but June 21st is also the day with the most amount of daylight in the Northern Hemisphere. Interestingly, our friends in the Southern Hemisphere will be simultaneously marking the winter solstice since their seasons occur opposite.
The term “solstice” comes from the Latin words “sol” (sun) and “sistere” (to stand still). At the solstice, the angle between the Sun’s rays and the plane of the Earth’s equator (called declination) appears to stand still. This phenomenon is most noticeable at the Arctic Circle where the Sun hugs the horizon for a continuous 24 hours, thus the term “Land of the Midnight Sun.”
Some people believe that our seasons are caused by the Earth’s changing distance from the Sun. In reality, it is due to the 23-degree tilt of the Earth’s axis that the Sun appears above the horizon for different lengths of time at different seasons. The tilt determines whether the Sun’s rays strike at a low angle or more directly. On July 4th at 3 a.m. EDT, the Earth will be at aphelion, its farthest point from the Sun in its orbit, at a distance of 94.5 million miles. Back on January 2nd, the Earth was at perihelion, closest to the Sun. The difference in distance is about 3.1 million miles, or 3.3 percent, which makes a difference of nearly 7 percent in radiant heat received by the Earth. It would seem that for the Northern Hemisphere, such a difference would tend to make for mild winters and cool summers, but the truth of the matter is, it actually works the other way, making winters colder and the summers hotter.
The summer solstice has long been celebrated by cultures around the world:
- In Ancient Egypt, the summer solstice coincided with the rising of the Nile River. As it was crucial to predict this annual flooding, the Egyptian New Year began at this important solstice.
- In centuries past, the Irish would cut hazel branches on Solstice eve to be used in searching for gold, water, and precious jewels.
- Many European cultures hold Midsummer celebrations at the solstice, which include gatherings at Stonehenge and the lighting of bonfires on hilltops.
Maybe you celebrate summer by taking a vacation or spending more time outdoors? Whatever you do, just remember, summer officially starts this June 21.