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Saturday, June 15, 2024

Earthsky Tonight Everything you need to know: June solstice 2010

The June solstice is your signal to celebrate the first day of summer in this hemisphere. South of the equator, winter begins.

When is the solstice where I live?

The solstice happens at the same instant for all of us, everywhere on Earth. However, our clocks say different times.

This solstice takes place on Monday, June 21, 2010 at 11:28 Universal Time. To find the time of the solstice in your location, you have to translate to your time zone.

Here is an example of how to do that. In the central United States, for those of us using Central Daylight Time, we subtract 5 hours from Universal Time. That is how we get 6:28 Central Daylight Time as the time of the 2010 June solstice.

Do you want to know the time in your location? Check out EarthSky’s article “How do I translate Universal Time into my time?” In addition, just remember: you are translating from 11:28 Universal Time, Monday, June 21.

What is a solstice?

The earliest humans 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 Stonehenge, to follow the sun’s yearly progress.

Today, we know that the solstice is an astronomical event, caused by Earth’s tilt on its axis, and its motion in orbit around the sun.

Because Earth doesn’t orbit upright, but is instead tilted on its axis by 23-and-a-half degrees, Earth’s northern and southern hemispheres trade places in receiving the sun’s light and warmth most directly.

At the June solstice, Earth is positioned in its orbit so that the North Pole is leaning 23-and-a-half degrees toward the sun. As seen from Earth, the sun is directly overhead at noon 23-and-a-half degrees north of the equator, at an imaginary line encircling the globe known as the Tropic of Cancer. This is as far north as the sun ever gets.

All locations north of the equator have day lengths greater than 12 hours at the June solstice. Meanwhile, all locations south of the equator have day lengths less than 12 hours

Where should I look to see signs of the solstice in nature?


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

If you live in the northern hemisphere, you can 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. Be sure to look at your noontime shadow. Around the time of the solstice, it is 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.

Why is the solstice a big deal?

Cultures universally have had markers, holidays and alignments . . . all related to the 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 is now England and aligned them with the June solstice sunrise.

We may never comprehend the full significance of Stonehenge. Nevertheless, we do know that knowledge of this sort was not isolated 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 June 21 and gazed toward the two pyramids, you would see the sun set exactly between them.

How does it end up hotter later in the summer, if June has the longest day?

People sometimes ask, “If June 21 is the longest day of the year, why is it that we usually receive the hottest weather not on that day, but in late July and August?”

This effect is called “the lag of the seasons.” It is the same reason it is hotter in mid-afternoon than at noontime. Earth just takes awhile to warm up after a long winter. Right now, 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 will come when the days are already beginning to shorten again, as Earth continues moving in orbit around the sun, bringing us closer to another winter.

And so the cycle continues.

Written by Deborah Byrd

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