Astronomy Essentials

2024 June solstice: All you need to know

June solstice: Four black-and-white satellite views of Earth, with different seasonal tilts.
Satellite views of Earth on the solstices and equinoxes. From left to right, a June solstice, a September equinox, a December solstice, a March equinox. Read more about these images, which are via Robert Simmon (Sigma Space Corporation)/ NASA.

When is it? A solstice isn’t a whole day. Instead, it’s a moment, when the sun is farthest north in our sky. In 2024, the solstice moment will fall at 20:51 UTC (3:51 p.m. CDT) on Thursday, June 20.
What is it? At the June solstice, the sun reaches its northernmost point. This point is on the celestial Tropic of Cancer, a parallel around the sky, 23.5 degrees north of the celestial equator. At this solstice, the Northern Hemisphere is most tilted toward the sun, by the maximum angle of 23.5°. The south is most tilted away, by the same amount.
What are its main effects? At the June solstice, no matter where you are on Earth, the sun rises and sets farthest north on your horizon. The sun is directly overhead at local noon as viewed from the Tropic of Cancer. Throughout the Northern Hemisphere, the sun is high in the sky and closest to being overhead at local noon.
What about day length?: For us in the Northern Hemisphere, the June solstice marks the shortest nights and longest days of the year. For the Southern Hemisphere, it marks the longest nights and shortest days. After this solstice, the sun will begin moving southward in our sky again.

What is a solstice?

Ancient cultures knew that the sun’s path across the sky, the length of daylight, and the location of the sunrise and sunset all shifted in a regular way throughout the year.

They built monuments such as the ones at Stonehenge in England and at Machu Picchu in Peru to follow the sun’s yearly progress.

Today, we know that the solstice is caused by Earth’s tilt on its axis and by its orbital motion around the sun.

The Earth doesn’t orbit upright with respect to the plane of our orbit around the sun. Instead, our world is tilted on its axis by 23 1/2 degrees. Through the year, this tilt causes Earth’s Northern and Southern Hemispheres to trade places in receiving the sun’s light and warmth most directly.

So it’s Earth’s tilt – not our distance from the sun – that causes winter and summer. In fact, our planet is closest to the sun in January, and farthest from the sun in July, during the Northern Hemisphere summer.

Night view of arches of huge rough-hewn vertical rocks with rocks lying across them. Crowd in foreground.
Waiting for dawn to arrive at Stonehenge, summer solstice 2005. Image via Andrew Dunn/ Wikimedia Commons/ CC BY-SA 2.0.

Signs of the June solstice in nature

Where should you look? Everywhere.

For all of Earth’s creatures, nothing is so fundamental as the length of the day. After all, the sun is the ultimate source of almost all light and warmth on Earth’s surface.

If you live in the Northern Hemisphere, you might notice the early dawns and late sunsets, and the high arc of the sun across the sky each day. You might see how high the sun appears in the sky at local noon. And, also be sure to look at your noontime shadow. Around the time of the solstice, it’s your shortest noontime shadow of the year.

If you’re a person who’s tuned in to the out-of-doors, you know the peaceful, comforting feeling that accompanies these signs and signals of the year’s longest day.

Two rows of brilliant star-like suns in a blue sky, one high and one low, through a circular open roof.
View at EarthSky Community Photos. | John Ashley was in Helena, Montana, when he created this composite image of 2 days of solstice suns in 2018. The uppermost line of suns is from that year’s summer solstice. The lower line of suns is from that year’s December solstice. John wrote, “The sun’s path during summer solstice arches high across the sky (upper), but at winter solstice it’s path barely clears the brick walls of the Potter’s Shrine, a sculptural landmark on the grounds of the Archie Bray Foundation in Helena, Montana. The interval composite photo was created over 2 days – months apart – by placing a fisheye lens on the ground and aiming it at the southern sky.” Thank you, John!

Is the June solstice the first day of summer?

No world body has designated an official day to start each new season, and different schools of thought or traditions define the seasons in different ways.

In meteorology, for example, summer begins on June 1. And every schoolchild knows that summer starts when the last school bell of the year rings.

Yet June 21 is perhaps the most widely recognized day upon which summer begins in the Northern Hemisphere and upon which winter begins on the southern half of Earth’s globe. Although, the June solstice can fall on June 20 or 22. There’s nothing official about it, but it’s such a long-held tradition that we all recognize those dates as the June solstice.

It has been universal among humans to treasure this time of warmth and light.

For us in the modern world, the solstice is a time to recall the reverence and understanding that early people had for the sky. Some 5,000 years ago, people placed huge stones in a circle on a broad plain in what’s now England and aligned them with the June solstice sunrise.

We may never comprehend the full significance of Stonehenge. But we do know that knowledge of this sort wasn’t limited to just one part of the world. Around the same time Stonehenge was being constructed in England, two great pyramids and then the Sphinx were built on Egyptian sands. If you stood at the Sphinx on the summer solstice and gazed toward the two pyramids, you’d see the sun set exactly between them.

Why doesn’t the longest day have the hottest weather?

People often ask:

If the June solstice brings the longest day, why do we experience the hottest weather in late July and August?

This effect is called the lag of the seasons. It’s the same reason it’s hotter in mid-afternoon than at noontime. Earth just takes a while to warm up after a long winter. Even in June, ice and snow still blanket the ground in some places. The sun has to melt the ice – and warm the oceans – and then we feel the most sweltering summer heat.

Ice and snow have been melting since spring began. Meltwater and rainwater have been percolating down through snow on tops of glaciers.

But the runoff from glaciers isn’t as great now as it’ll be in another month, even though sunlight is striking the Northern Hemisphere most directly around now.

So wait another month for the hottest weather. It’ll come when the days are already beginning to shorten again, as Earth continues to move in orbit around the sun, bringing us closer to another winter.

And so the cycle continues.

Animated view of Northern Hemisphere from orbit with ice coverage expanding and contracting.
Check this out … the Breathing Earth. It’s a year of seasonal transformations on our planet, including the June solstice. John Nelson created this animation, using images from the NASA Visible Earth team. Read more about the animation via John Nelson.
People in field standing behind each other with arms outstretched with sun behind them.
Hello, summer solstice! Image via Abigail Hart.

Bottom line: The 2024 June solstice will happen on June 20 at 20:51 UTC. That’s 3:51 p.m. CDT in North America. This solstice – the beginning of summer in the Northern Hemisphere – marks the sun’s most northerly point in Earth’s sky.

Visit EarthSky’s night sky guide.

Why the hottest weather isn’t on the longest day

Posted 
June 19, 2024
 in 
Astronomy Essentials

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