Ah, summer. The season of swimming, relaxing, and lazy days in the sun arrives this Sunday, June 21, the summer solstice for the Northern Hemisphere.
So what is a solstice, exactly? It’s the result of Earth’s north-south axis being tilted 23.4 degrees relative to the ecliptic, the plane of our solar system. This tilt causes different amounts of sunlight to reach different regions of the planet during Earth’s year-long orbit around the sun.
On Sunday, the North Pole is tipped more toward the sun than on any other day of 2015. (The opposite holds true for the Southern Hemisphere, where it will be the winter solstice, the shortest day of the year.)
Read on for some more intriguing facts about the summer solstice.
More Sunlight Doesn’t Mean More Heat
On the summer solstice, the Northern Hemisphere receives more sunlight than on any other day of the year—but that doesn’t mean the first day of summer is also the hottest.
Earth’s oceans and atmosphere act like heat sinks, absorbing and reradiating the sun’s rays over time.
Even though the planet absorbs a lot of sunlight on the summer solstice, it takes several weeks to release it. As a result, the hottest days usually occur in July or August. (See National Geographic’s best summer trips for 2015.)
“If you think about turning up an oven, it takes it a long time to heat up,” explains Robert Howell, an astronomer at the University of Wyoming.
“And after you turn it off, it takes awhile for it to cool down. It’s the same with the Earth.”
The Earth Isn’t Any Closer to the Sun
Another popular misconception is that during the summer—and especially during the summer solstice—Earth is closer to the sun than at other times of the year, says Mark Hammergren, an astronomer at the Adler Planetarium in Chicago.
In reality, the tilt of the Earth has more influence on the seasons than does our planet’s distance to the sun.
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