On this date (approximately), the first June solstice occurred on Earth. It has happened with each revolution of the Earth around the Sun since then.
The June solstice occurs because Earth doesn’t orbit the Sun upright. Instead, our world is tilted on its axis by 23-and-a-half degrees, and as a result, Earth’s Northern and Southern Hemispheres trade places in receiving the sun’s light and warmth most directly. If the Earth’s rotation was at right angles to the plane of its orbit around the sun, there would be no solstice days and no seasons.
At the June solstice, Earth is positioned in its orbit so that our world’s North Pole is leaning most toward the sun. As seen from Earth, the sun is directly overhead at noon 23 1/2 degrees north of the equator, at an imaginary line encircling the globe known as the Tropic of Cancer – named after the constellation Cancer the Crab. This is as far north as the sun ever gets.
All locations north of the equator have days longer than 12 hours at the June solstice. Meanwhile, all locations south of the equator have days shorter than 12 hours.
The varying dates of the solstice are mainly due to the calendar system – most western countries use the Gregorian calendar, which has 365 days in a year, or 366 days in a leap year. As for the tropical year, it is approximately 365.242199 days, but varies from year to year because of the influence of other planets. A tropical year is the length of time that the sun takes to return to the same position in the cycle of seasons, as seen from Earth. The exact orbital and daily rotational motion of the Earth, such as the “wobble” in the Earth’s axis (precession), also contributes to the changing solstice dates.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 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 the summer solstice and gazed toward the two pyramids, you’d see the sun set exactly between them.
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.