The summer solstice is coming! Here’s what to know

by Melissa Breyer (@MelissaBreyer)
Science / Natural Sciences


The 2017 solstice falls on June 20 or June 21 depending on where you are … celebrate with a crash course in curiosities about the longest day of the year.

It’s hard to believe that a mere six months ago, those of us in the Northern Hemisphere were grimly facing the shortest day of the year – and now suddenly, the sun is setting at bedtime and the unofficial first day of summer is upon us! How did that happen?! To be honest, the winter and summer solstices sometimes feel out of whack with the seasons they represent – shouldn’t the longest day of the year be the hottest and occur at the height of summer? Answers to that curiosity and more explained below.

(Note: For the Southern Hemisphere this is all reversed, thanks to our topsy-turvy world.)

1. First things first, the when of it all
In North America this year we can revel in longest period of sunlight on Wednesday, June 21 at 12:24 AM. EDT. This is the precise moment when, basicly, the sun stands still at its northernmost point as seen from Earth. Its zenith doesn’t teeter north or south, but sits patiently at the Tropic of Cancer before switching directions and heading south again. This is where the word solstice comes from; the Latin solstitium, from sol (sun) and stitium (to stop).

Since this happens at a specific moment in the heavens, it happens at the same time across the time zones – which means that for some, it falls on June 20.

CDT: June 20, 11:24 PM.
MDT: June 20, 10:24 PM
PDT: June 20, 9:24 PM

2. There will be SO MUCH SUNLIGHT
Get your sunglasses out, bare your shoulders, put on the sunscreen! The weatherman willing, we will have oodles of sunlight. In New York City, we will have a soul-affirming 15.05 hours of daytime. (You can check your day length at the Farmer’s Almanac sunrise and sunset calculator, to see what to expect in your neck of the woods.)

3. The longest day isn’t the hottest
Given that the sun passes directly overhead on the solstice – and it’s the day with the most sunlight – one wouldn’t be off-base to think it might claim the highest temperatures as well. But no. As NOAA explains, in the US, temperatures continue to inch up into July. “The temperature increase after the solstice occurs because the rate of heat input from the sun during the day continues to be greater than the cooling at night for several weeks, until temperatures start to descend in late July and early August.” The map below, based on 30 years of data, is a few years old but still gives a good indication of what to expect where.

warmest day© NOAA

4. The north gets short-changed on summer sun
While it certainly may not feel like it, in the Northern Hemisphere’s summer we are actually farthest from the sun thanks to the planet’s tilt; we get 7 percent less sunlight than the Southern Hemisphere does during their summer. Something we’ll be grateful for in a few billion years (see #8).

5. The constellation of Cancer steals the spotlight
The Tropic of Cancer is so-named because waaaay back when during the ancient naming of these things, the solstice sun appeared in the constellation Cancer. Due to subsequent shifting of Earth’s axis, explains Discovery, the Tropic of Cancer is now misnamed. This year on the June solstice, the sun will actually be moving from constellations Gemini to Taurus.

6. Lots of sunlight, but a dark day for science
According to legend, Galileo was, rather ironically, forced to recant his theory that Earth revolves around the sun on the summer solstice of 1633.

7. It’s a day of celebration
The solstice has been such a vastly important day throughout history that it would be impossible to list all the significant celebrations here. From Stonehenge on, the day is more-so-than-not marked by revelry – including no shortage of libations, nudity, dancing in the woods, costumes, parades, bonfires and general merrymaking.

8. The future of the summer solstice is bright. Really, really bright
The gifts of the sun have been a cause for celebration for millennia – and as it turns out, based on models of stellar evolution, the sun is about 40 percent more luminous today than it was when the Earth was born some 4.5 billion years ago. And it doesn’t look like it’s going to slow down. Scientists estimate that in another 1 billion to 3 billion years, the sun’s looming intensity will “boil away Earth’s oceans, turning our planet into an endless desert,” notes Discovery. In which case, the winter solstice will surely become the day to frolic naked in the forest…