The summer solstice of this year is in front of us: the 20th and 21st of June will be the longest days of this year for anyone that is living north of the equator. If pagan rituals are your thing, this will probably be a big moment for you. If not, the solstice is still pretty neat.
Generally speaking, the summer solstice happens when the sun is directly overhead at the Tropic of Cancer or 23.5° north latitude. In 2018, this happens at exactly 12:24 am (Eastern) on the 21st of June, but we can celebrate it every single day. Here, we have little scientific evidence and guide for the longest day of the year, though not, as we will see, the longest day in the history of the planet Earth, which has happened back in 1912.
1. Anyway, why do we have a summer solstice?
A lot of people know this one. The Earth orbits around the sun on a tilted axis. It could be a result of a collision with some other massive object billions of years ago during the creation of the earth. So, between March and September, the Northern Hemisphere of our planet gets more exposure to direct sunlight over the course of the day. The rest days of the year, the Southern Hemisphere gets more. It is the reason for the four seasons:
So between March and September, the Northern Hemisphere of the Earth will get more exposure to direct sunlight during one day. The rest of the year, the Southern Hemisphere receives more. It’s the reason for the seasons: spring, summer, autumn, and winter. In the Northern Hemisphere, the “peak” sunlight often happens on the 20th, 21st, or 22nd of June of any year. That is the summer solstice. On the contrary, the Southern Hemisphere reaches peak sunlight on the 21st, 22nd or 23rd of December, and the north hits peak darkness, that is our winter solstice.
2. How many hours of sunlight will we get on that day?
It depends on where we live, the further north you are the more sunlight you will see during the solstice. The Alaska-based climatologist Brian Brettschneider created a traffic guide shown below.
If you are living somewhere around the Arctic Circle, the sun never really sets down at a time of the solstice. Opposite of this, during the winter solstice, Fairbanks only gets about three hours of sunlight.
Here, we are going to present you another cool way to visualize the extreme of the summer solstice. In 2013, one resident of Alberta, Canada, took a pinhole camera photographer of the path of the sun throughout the year, and he shared it with the astronomy website EarthSky. There can be seen a dramatic change in the arc of the sun from December to June.
Also, you should notice that the solstice gives us the longest twilight of the year, often 1 to 1.5 extra hours after sunset.
3. Will the solstice be the latest sunset of the year?
Not necessarily. Just because the 20th of June will be the longest day of the year for the Northern Hemisphere, it does not mean that every location has its earliest sunrise or latest sunset on that day.
For instance, if you live in Washington DC, you can see the earliest sunrise, as it will occur on the 13th of June. Also, you can catch the latest sunset on the 27th of June. If you are sleep-lover, that means that day will probably be the most exciting one of the summer.
4. What is the connection with Stonehenge?
No one still knows why men built Stonehenge some 5,000 years ago. But, there is one possibility that it was used to mark solstices and equinox. That is why during the summer solstice, the sun rises just over the structure’s Heel Stone and hits the Altar Stone dead center. Nowadays, people still gather to pay homage to the summer solstice at Stonehenge; they are just using modern technology.
5. Is this the longest day in the entire history of our planet?
It is probably not, but it is close. This is also the reason why it is quite impressive. Joseph Stromberg did a fantastic deep dive into this topic for Vox several years ago.
Ever since our planet has had liquid oceans and a moon, its rotation has been gradually slowing over time because of the tidal friction. That actually means that the days have been getting steadily longer. About 350 million years ago, it took only 23 hours, but today, of course, it takes 24. And the days are going to get longer gradually.
But, the tidal friction is not the only thing which affects the rotation of Earth – there is also the melting of glacial ice, which has been happening since the end of the last ice age which was 12,000 years ago. It actually speeds up the rotation of the planet, shortens the days by a few fractions of a millisecond.
When we put all these factors together, it appears that the longest day in Earth’s history likely happened in 1912. In that year, the summer solstice was the longest period of daylight in the Northern Hemisphere has ever seen.
6. Is there going to be a solar eclipse too?
There won’t be on this solstice. But, there is going to be a rare solar eclipse across the entire continental US a bit later in the summer, on the 21st of August. On that day, the Earth, as well as the moon and sun are going to be perfect alignment to cast a 60-mile-wide shadow which is going to trace itself across the country like a dark laser pointed on a whiteboard.
In the bull’s eye center of the shadow of the moon which is known as the totality, the sky is going to go dark for several minutes in the middle of the day, the stars will appear, and the birds will become confused and start chirping their nighttime songs. That is all a result of cosmic coincidence: From the Earth, both the moon and sun seem to be roughly the same size.