In the Northern Hemisphere the longest day of the year falls on 21st June. This day is often referred to as the Summer Solstice or Midsummer’s Day. But why is this day so much longer than average?
As the Earth rotates on its axis, parts of the world move closer to the sun, while the rest moves farther away. It is this tilt which brings it nearer to the Sun that is force behind the solstice. On 21st June the Earth’s axis tilts 23 degrees at the same time as the Sun reaches its highest point of altitude. The result is that, with the exception of the Polar Regions, the Northern Hemisphere experiences the longest period of daylight hours of the year on that day.
In the UK and Europe the longest day is usually 21st June, but due to the curvature of the Earth, the highest altitude of the Sun occurs on a different day in a few locations over the tropics. In areas where the sun is directly overhead (within both the Tropic of Cancer and the Tropic of Capricorn) there are two different ‘longest’ days. This is because the Sun crosses directly once on the day before the solstice and once on the day after.
Occasionally the summer solstice falls on June 22nd in Europe; although it is very rare. The last time this happened was 1975 and the next time will be in 2203. This occasional variation of a day, or a few days as you get nearer the equator, is because the earth orbits the sun in an ellipse and not a circle (or sphere), and its orbital speed varies slightly during the year.
The Winter Solstice, or the shortest day, which occurs on the 21st December in the Northern hemisphere, works in the opposite way. The Earth is orbiting at its furthest point from the Sun, and so we experience long periods of dark skies and therefore a shorter day.
The longest day traditionally marks the first day of summer in the UK, just as the 21st December heralds the start of Winter. However, just because the Summer Solstice is the longest day, it does not guarantee that it will be the hottest, or even warm. Traditionally the Summer Solstice has been a time to celebrate the planting and harvesting of crops. This ancient idea is still celebrated by some to this day; most famously commemorated in England by the Druid communities who gather near Stonehenge to watch the sun rise over the Heel Stone.
Dr Kathryn Bates is a graduate of archaeology and history. She has excavated across the world as an archaeologist, and tutored medieval history at Leicester University. She joined the administrative team at Oxford Open Learning twelve years ago. Alongside her distance learning work, Dr Bates is a bestselling novelist, and an itinerant creative writing tutor for primary school children.