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What is the summer solstice and what does that have to do with the longest day of the year? Here’s a quick look at what it means.
What is it?
The solstice happens when the sun reaches the highest point in the sky relative to the equator, meaning the Northern Hemisphere is tilted fully toward the sun. In fact, the North Pole is tilted far enough toward the sun to where the Arctic Circle will see 24 hours of daylight.
The sun reaches its northernmost point on Earth during the summer solstice. Do you know where that is?
The sun will reach its northernmost point when it hits 23 degrees 27 minutes north latitude – in the Tropic of Cancer.
When does it do that?
In 2019, the solstice falls on Friday at 11:54 am ET.
Wait, isn’t it on the same day every year?
The summer solstice happens each year between June 20-22.
Why isn’t it on the same day every year?
Blame it on math. The fact that the date floats is due, in part, to the difference between the Gregorian calendar system, which normally has 365 days, and the tropical year (how long it takes Earth to orbit the Sun one time), which is about 365.242199 days, according to The Farmer’s Almanac.
The Georgian calendar adds a leap day every four years to make up for the extra .242199. The leap day, along with other factors, moves the summer solstice backward and forward on the calendar by a couple of days.
Why is it the longest day of the year?
It’s known as the longest day of the year not because it’s any longer than any other day, but because in the Northern Hemisphere, it’s the day that receives the most hours of daylight. It receives the most sunlight because the Earth is tilted toward the sun for the longest time during a day.
If it is the longest day of the year and it’s summertime, why isn’t it the hottest day of the year?
It's not the hottest day of the year because the Earth releases the energy it absorbs at various rates – but it never releases it instantly. On Friday, the Earth will receive the most energy from the sun, but will release that energy in late July or August, usually. This effect, according to Weather Works, is called seasonal temperature lag.