The Reason for the Longest Day Summer Solstice
Since time immemorial people have been asking the question, why is the summer solstice, which occurs in the northern hemisphere around the 20-21 June, the longest day of the year? In reality, a number of factors contribute to the changes in daylight that we witness throughout the year and cause the longest day to occur, and indeed the shortest day together with all the variation of daylight lengths in between these times of the year.
As all will know, the earth rotates on its axis, which is a good idea otherwise we would all fall off. However, that axis is not perpendicular, but rather some 23.5 degrees off centre. Scientists think that this angle was created some five billion years ago, possibly resulting from the earth being hit by a large meteorite. Of course, you could argue that God decided that he did not want the earth to be perfect and tilted it himself.
The earth's orbit is also a contributory factor to the length of daylight that we receive at various times throughout the year. Because this orbit is not a perfect circle, being more of an elliptical shape, the distance between the earth and the sun changes during the orbit. It is estimated to alter between 91.5 million miles in March and September and 94.5 million miles in December and June. The greater the distance the sun is from the earth then the wider the circle of light that it sheds over the earth, in the same way that the closer you place a torch light to an object, the smaller the circle of light it creates, and visa versa when you pull that torch back from the object.
The summer solstice in June is therefore created by a combination of the angle of the earth's axis and the position of the earth in its orbit around the sun. At that time of the year, the northern hemisphere is tilted towards the sun when it is at its furthest distance from our planet. Looking at it as we stand on the earth, the sun is at its highest point in the sky, in fact directly above the equator, and therefore takes longer to travel the distance that we recognise as being between sunrise and sunset, thus causing the daylight to last longer. It is on the summer solstice that this journey of the sun across the sky takes the most time, which therefore creates the longest day.
Even within the Northern Hemisphere the daylight hours will differ during the summer solstice. For example, at the equator there will be no difference to its continual twelve-hour sunlight, twelve-hour darkness routine. However, as one travels north from the equator though, the summer solstice daylight hours increase the closer one gets to the North Pole. In fact, in parts of Alaska and the North Pole itself there is twenty-four hour daylight during the summer solstice. Conversly, the position is totally opposite in the Southern Hemisphere. When we in the north are enjoying the summer solstice, those in the south will be wrapping up for the winter solstice and finding the nights longer. In fact, the South Pole at this time will be witnessing total darkness throughout the day.
Although we may wish the summer season to be longer, we should actually consider how lucky we are that the earth's tilt and orbit of the sun is the way it is. For if the Earth's axis did not tilt, areas and nations close to the poles would be in darkness and cold for the whole year. Conversely, if the tilt was much greater than the 23.5 degrees we would be experiencing even more severe seasonal adjustments. For example, consider the problems of living on a planet like Uranus, where the winter and darkness lasts for forty-two years. On reflection, I think I prefer it here!
