The 2019 summer solstice will arrive in the northern hemisphere this week. The summer solstice is the point in the year when Earth’s north pole tilts furthest toward the Sun. Technically, the solstice takes place at a specific point in time, which this year will be 4.54pm BST (11.54am EDT) on Friday, June 21, according to the Old Farmer’s Almanac.
But when the solstice more commonly refers to the entire day on which it lands.
The solstice is the longest day of the year in the northern hemisphere – as it has the most hours of sunlight.
There will be 16 hours and 38 minutes of daylight in the UK, and the Sun will rise at 4.43am before setting at 9.21pm.
This is because our Sun will appear at its highest in the northern sky, directly over the Tropic of Cancer.
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Those living in the southern hemisphere conversely experience the shortest day of the year with the least sunlight hours.
Earth experiences solstices because the planet is tilted on its axis by 23.5 degrees relative to the plane of its orbit.
Each hemisphere consequently experiences six months tilted toward the Sun and the other half tilted away from our star.
The differences in the tilt mean both hemispheres are struck by varying levels of radiation from the Sun over the course of the year, creating the seasons.
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So when the northern hemisphere is tilted toward the sun, it experiences summer because radiation from the star is striking it at a more direct angle.
As you move closer to the equator, this effect becomes less noticeable.
This is why the equatorial region does not really experience the seasons, as the Sun’s radiation striking the area is more constant.
In astrological terms, the June solstice marks the end of spring and start of summer for the northern hemisphere.
And this season will end with the autumn equinox, occurring on September 23.
However, when speaking in meteorological terms, summer actually begun on June 1 and will end on August 31.
The meteorological year is defined differently to the astrological year, taking the months of the calendar and annual temperature cycles into account.
The summer solstice does not always fall on the same date and can actually occur any time between June 20 and 22.
This is because to slight variations in the widely-used Gregorian calendar, which has 365 days, and the solar year, the time it takes for the Earth to complete one revolution around the sun (365.242199 days.)
To ensure the calendar is synchronised with the seasons, we add an extra day to the year around every four years what is commonly called a leap year.