The summer solstice is the day when the sun is at its northernmost point

Some astronomical facts about the longest day of the year, when the Earth reaches the summer solstice. The sacrifice between him and the arrival of the earth at the farthest point from the sun and at the Stonehenge site 

The summer solstice heralds the beginning of summer in the Northern Hemisphere. The moment of solstice is when the sun reaches (from the point of view of observers on Earth) its northernmost point from the equator (ie the northern hemisphere is at its maximum inclination towards the sun). In 2015, summer will begin at the moment of the solstice, on June 21 at 19:38 GMT.

The English term for the solstice, solstice, comes from the Latin word solstitium - sol (the sun) and - stitium (to stop), a phrase that reflects the observation that the sun stops at that time (and so also on the winter solstice). In low latitudes, the sun is high in the sky during the day, and its rays strike the earth at an almost right angle. Due to the increase in solar radiation, the air heats up and we call this period summer. On the day of the winter solstice, the situation is reversed: the sun is at the southernmost point and is therefore low in the sky. Rays strike the northern hemisphere at a sharp angle. In northern countries in particular, this phenomenon causes the sunlight to be weaker.

These days the Earth is near the furthest point in its orbit around the Sun (ephelion). In fact the Earth will reach aphelion two weeks after the longest day of the year, on July 6, 2015, at 16:41 GMT. At this point its distance from the Sun is 152,097,700 kilometers. At the point closest to the Sun (the perihelion) it was this year on January 4, 14 days after the winter solstice of 2014. Its distance at this point is 148,098,070 kilometers from the Sun.

The reason why the Earth reaches the Phirelion shortly after the winter solstice in recent centuries is due to the way the Gregorian calendar adjusts the solstice days. While the days of the solstices do not vary that much (around December 21st and June) the date when the Earth is at its closest or furthest point from the Sun varies over a much wider range. The last time the December solstice occurred exactly when the Earth was at perihelion was in 1246.

The dates of the Earth's arrival at the perihelion and aphelion points in its orbit around the Sun are not fixed due to the variation in the eccentricity (degree of ellipticity) of the Earth's orbit. In fact, the time when the Earth reaches perihelion or ephelion in its orbit changes by one day every 58 years. Mathematicians and astronomers have calculated that in the year 6430, in almost 4,000 years, the timing of the perihelion and the equinox of March will be equal.

One of the places most associated with celebrations on the days of the solstice and the days of the equinox is the Stonehenge site, an ancient prehistoric site in England that contains the remains of a multi-columned structure that served as a sort of agricultural astronomical table with which the local residents calculated the seasons more than 4,000 years ago. According to the official website, Stonehenge has been used since ancient times as a site for religious ceremonies and events.

During the days around the summer solstice The site administration opens (English Heritage Association) the place for individuals and groups wishing to hold ceremonies and celebrations as they wish (with the exception of course of general prohibitions).

Inflection point - Wikipedia

More on the subject on the science website

• Why do the seasons change?
• The summer solstice - a short lesson in astronomy
• A summary of the history of time - the first part of the overview of the measurement of time throughout history by Amnon Carmel (including details about Stonehenge)