Summer solstice is the longest day of the year but it won’t be the hottest
You probably haven’t noticed it yet, but the days are already starting to get shorter. Even though we’ve hardly had much of what could be called “summer weather” in our local area this year, we are now past the longest day of the year, which occurred yesterday, June 21.
This day, which is also the official first day of summer, is called the solstice from the Latin words for “sun” and “to stand still.”
The reason for this name is that the sun appears at a higher angle in the sky each day throughout the spring until it “stops” and then starts to reach only lower angles in the sky on subsequent days.
At the same time, the number of hours of sunlight in a day gradually increases each day to the point where it reaches its maximum on the solstice, and then the days start to get shorter.
While yesterday was the longest day of the year (summer solstice) in the northern hemisphere, it was also the shortest day of the year (winter solstice) in the southern hemisphere. Similarly, when we have our winter solstice on our shortest day of the year in December, that day will also be the summer solstice and the longest day of the year in the southern hemisphere.
The change in the length of days throughout the year and the variable angle of the sun in the sky are two manifestations of the same phenomenon, caused by a tilt in the Earth’s axis of rotation.
This imaginary line through the North and South poles around which the Earth turns is angled (by about 23.5 degrees) relative to the plane in which the Earth revolves around the sun. This means that at some times of the year the northern end of the axis is titled towards the sun and at other times it is tilted away.
When the northern end of the Earth’s axis is tilted towards the sun, the sun appears to be higher in the sky in the northern hemisphere. On the day of the northern summer solstice, the Earth is at the place in its orbit around the sun where the axis is most directly pointed towards the sun, resulting in the sun appearing to be the highest in the sky that it reaches all year.
Indeed, if you are far enough north, you may even see the Midnight Sun, where the sun never drops below the horizon on that day.
Of course, if the northern end of the Earth’s axis is tilted toward the sun, the southern end of the axis is also tilted away, which is why the longest and shortest days of the year in the northern and southern hemispheres occur on the same day.
You might ask yourself, since we are now getting the most hours of sunlight in a day and the sun is at its highest point in the sky, why haven’t the days reached their hottest temperature of the summer? It would seem logical that the days with the most sunlight should be the hottest, but this is not the case – the shorter days of July and August reach much hotter temperatures than what we experience at the end of June.
The reason for this is that it takes quite a long time for the landmass, water and air to warm up.
The local temperatures have been gradually rising since the winter and throughout the spring, but this takes longer than the change in the length of the days. As a result, there is a lag time of several weeks during which the ground, water and air continue to warm up even though the amount of sunlight is starting to decrease.
This warming and cooling cycle of the seasons is punctuated throughout the year by predictable days like the summer and winter solstices, which mark the starts of the various seasons.
Civilizations since ancient times have kept track of these days with a variety of calendars. One of the best known of these is Stonehenge in England, but everything from the pyramids in Egypt to castles and cathedrals in western Europe have been aligned so that the rising or setting sun on the solstice day could be observed each year. These observations helped to determine the dates for a variety of religious and pagan rituals marking the passage of the seasons.
In our modern culture, the first day of summer brings its own rituals, such as the end of the school year, and the start of the vacation season. Let’s hope that now that the first day of summer has finally arrived, we will get lots of barbecue and beach weather in the days to come.