The summer solstice marks the beginning of longer days filled with backyard barbeques, tropical vacations, and, of course, the summer sun. That said, this year’s solstice looks a bit different than years past. Discover why Earth’s days are expected to be longer than ever this summer, ahead.
When is the summer solstice?
The summer solstice varies from year to year but typically occurs between June 20th and June 22nd. This year, the solstice takes place on June 21st.
What is the summer solstice?
In a nutshell, the summer solstice marks the beginning of the astronomical summer season when the Earth is farthest from the sun, and the Northern Hemisphere leans towards it.
During this period, the tilt of the Earth’s axis changes to about 23 degrees in relation to its usual orbital path around the sun. Though slight, the tilt makes a big difference here on Earth, marking mid-summer in the Northern Hemisphere and mid-winter in the Southern Hemisphere.
In addition to being the official astronomical start to the summer season, the summer solstice also happens to be the longest day of the year. On the solstice, the sun’s path arcs higher and takes longer to travel across the sky than any other day of the year. According to Timeanddate.com, this sequence happens “when the sun is directly over the Tropic of Cancer in the Northern Hemisphere.”
Why Earth’s days are longer than ever this summer solstice
The Earth’s days weren’t always 24 hours. According to National Geographic, at one point — 1.4 billion years ago, to be exact — Earth’s days were only about 18 hours long. The lengthening of days has to do with the gravitational pull between Earth and the moon.
For billions of years, the moon has caused the ocean’s tide to rise and, while the moon is busying orbiting Earth, it pulls the tide with it, creating a dragging effect that slows down the Earth’s rotation. Because the moon was once a lot closer to Earth, it’s gravitational pull — or, drag — was a lot stronger, causing shorter days.
Today, the moon prefers some more personal space, falling farther away from the Earth’s orbit at about 3.8 centimeters per year. Given that this is about the same speed fingernails grow, it doesn’t seem like much. However, over time 3.8 centimeters can add up — after all, that’s how we went from 18-hour days to 24-hour days.
What does all of this have to do with this year’s summer solstice? For starters, the Earth and the moon are farther apart than they were this time last year, so the days are slightly longer. As the longest day of the year, the 2018 June solstice is one of our longest yet.
Following the solstice, the days are still long, but over time they begin to decrease. At this time, the sun slowly lowers its path until it reaches 12 hours of daylight. This shorter day marks the autumnal equinox.
Check out The Cheat Sheet on Facebook!