June 21 marks the Summer Solstice for the Northern Hemisphere this year. As the Earth orbits the sun, the tilt of the planet and its elliptical orbit combine to create the seasonal changes in daylight and temperatures we experience every year.
The term “Summer” has different definitions. Scientists who track weather and climate data need well-defined and consistent date ranges for seasons, which make it easier to compare one year (or one season) to the next for commerce or agriculture. For this reason, the “Meteorological” season of summer runs from June 1 to August 31 every year.
Astronomers, however, mark the seasons based on the position of the Earth relative to the sun, and these can land on different days of the year. The June solstice, usually June 20 or 21, is the date on which the North pole points directly towards the sun. On this day, all points north of the Arctic circle experience 24 hours of daylight, as the sun circles the sky without setting. This is the beginning of Astronomical Summer, which ends on the Autumnal Equinox in September.
Another factor that affects temperatures is Earth’s orbit around the sun. In June, Earth reaches aphelion, or the point in its orbit when we are farthest from the sun. Over the entire planet, this means there are lower average temperatures than at other times of the year. However, the North Pole is also tilted toward the sun, providing the Northern Hemisphere with more hours of sunlight than any other time. The sun angle contributes more to the local temperatures than the distance from the sun, so the longer summer days bring much warmer weather than the short days of winter.
Throughout history, the Summer Solstice has been marked by celebrations and festivals. It is sometimes referred to as “Midsummer” in Northern Europe, and some Neopagan groups call it “Lithia.” Pre-Christian pagans from ancient Central and Northern Europe used to “ring in” Midsummer with bonfires, hoping for a good growing season and harvest.
In ancient Greece, the Solstice had special significance as the first day of their calendar year, and the start of a one-month countdown to the Olympic games. In ancient China it was also special, and was connected to “yin,” the feminine force. The Vikings observed the event by gathering to discuss disputes and other legal matters.
Some Midsummer festivals and rituals are still observed today, including a few practiced by Native Americans such as the Sioux, who perform a ceremonial sun dance. Northern Europeans still light bonfires, and the solstice is a popular date for weddings in many cultures. Across the United States, art or music festivals are popular events, as are family gatherings.
One of the largest modern celebrations of the solstice takes place at Stonehenge, in Wiltshire, England. Also called a “Giant’s Dance”, Stonehenge (built around 2500 BCE) is arranged so the rising sun lines up with particular spots at significant astronomical events during the year, particularly Midsummer. This arrangement has led some historians to believe the builders used the dance as an early form of a calendar.
In recent years, lengthening days and lots of sunlight have been found to be associated with positive moods and a reduction in depression and anxiety. For about a month before and after Midsummer each year, the Northern Hemisphere will have exceptionally long days. Because the change in day length becomes smaller and smaller before reversing on the solstice, expect a full week of exceptionally long days centered on June 21 this year. Enjoy the sunlight, and consider celebrating with a family gathering around a bonfire!