Saturday, June 21, marks the first official day of summer in the Northern Hemisphere, when the sun reaches its northernmost point in the sky.
But did you know that the summer solstice, as it’s called, is the longest day of the year?
Here are five facts to know about the first day of summer.
When does the summer solstice begin, exactly?
In the Northern Hemisphere, the summer solstice begins at 6:51 a.m. EDT on June 21, according to Almanac.com, officially ringing in summer. The date brings the year’s longest stretch of daylight. Though the hours of sunlight depend on location, many areas will see 16 hours’ worth of light on Saturday.
Why does the solstice occur?
The word solstice is from the Latin solstitium from sol (sun) and stitium (to stop), because it appears the sun stops at the solstice. The solstice happens twice annually due to the Earth’s axis of rotation. Depending on the calendar year, the summer solstice happens annually in December for the Southern Hemisphere and on June 20 or 21 in the northern half of the world.
For science aficionados, the summer solstice occurs precisely when the Earth’s axial tilt is most inclined toward the sun, at the degree of 23° 26′, its most extreme. In June, the tilt is toward the sun in the Northern Hemisphere, while the second yearly solstice, the winter solstice, in December, the tilt is away from the sun in the Southern Hemisphere.
How is the solstice celebrated?
The solstice marks the first day of summer in the Northern Hemisphere, and that means flip-flops, beach trips and barbecues. In southern England, thousands flock to Stonehenge to see the sun rise from the vantage point of the 4,000-year-old solar monument.
The summer solstice is also a time of celebration for Christians and Pagans. In Christianity, the first day of summer marks the festival of St. John the Baptist, and in Paganism followers celebrate what they call “midsummer” with bonfires and feasts.
Is it the longest day of the year?
The summer solstice has the longest hours of daylight for the Northern Hemisphere, Time And Date reported. The sun, which usually rises directly in the east, rises north of east and sets north of west. This means the sun is in the sky for a longer period of time, yielding more daylight.
Why do the warmest days of summer generally come long after the solstice?
According to Space.com, it takes a month or two for some geographic areas to see their warmest days simply because it takes the Earth time to warm up. In fact, solstices do not mark the start of winter or summer at all; they are actually the midpoint of each season.
Almanac.com calls this phenomenon, when the land and oceans release stored heat back into the atmosphere much later than the first day of summer, the “seasonal temperature lag.”