Welcome, Summer: The Science Behind Saturday's Solstice and the Longest Day of the Year
This Saturday, June 21, marks the summer solstice in the Northern Hemisphere, the day with the most daylight hours and the official astronomical start of summer. This annual event is a direct result of our planet's celestial mechanics, a moment determined by the Earth's unique tilt as it journeys around the Sun.
The solstice occurs because the Earth revolves on a slanted axis. At this specific point in its orbit, the Northern Hemisphere is tilted most directly toward the Sun. This alignment positions the Sun at its highest point in the sky, directly over the Tropic of Cancer. This maximum tilt gives us our longest period of daylight. In regions within the Arctic Circle, the effect is even more dramatic, resulting in the "midnight sun," where daylight is continuous for several days.
Interestingly, while the solstice is the longest day, it doesn't feature the earliest sunrise or the latest sunset of the year. These occur a few days before and after the solstice, a quirk caused by the shape of Earth's elliptical orbit and its variable speed. Similarly, the warmest weather of the summer usually arrives weeks later. The ground and oceans absorb the sun’s energy slowly, taking time to heat up and raise air temperatures.
The term "solstice" comes from the Latin words "sol" (sun) and "sistere" (to stand still), reflecting how the sun appears to pause at its northernmost point before beginning its slow journey south again. While the date can vary between June 20 and 22 due to our calendar's leap-year cycle, its arrival is a reliable and welcome signal of the warm-weather days to come.
Image source: Time and Date
