The summer solstice arrives Sunday afternoon. If you are an astronomer this marks astronomical summer or the time when the sun’s rays are most direct across much of the northern hemisphere.
From this point forward, until the winter solstice, the sun’s position in the sky will slowly be progressing further south and lower. Additionally, there will be a loss of net daylight starting Monday.
Warmest Yet To Arrive
If you only think of summer by the position of the sun, the 21st of June can mark the beginning of the end. However, there is still plenty of warm weather ahead. On average the warmest period of the year is still about a month away. This is because, in spite of small losses in the amount of solar heating during the rest of June and July, there is still so much of incoming ultraviolet light, the earth continues to heat up for several weeks past the solstice. The atmospheric temperatures in this part of the word really won’t respond to the loss of ultraviolet light until early August. (the opposite is true with cold and the winter solstice).
July is a mid-summer month in the same way January is a mid-winter one. In July, in spite of the loss of nearly an hour of daylight it’s still very warm. In January, in spite of gaining nearly an hour of light, it’s still very cold.
What I enjoy watching is the changing position of the sun. Take a look at where the sun rises and sets this time of year. Imagine you are at the center of a pie cut into 8 slices. If you watch the sun come up, look to your right one slice of the pie, now look a little further. That’s where the sun will come up in December. Put another way, the position of the sun will move about 50 degrees to the right over the next 6 months. The same thing is true in the evening. Note the position of the sun as it sets over the next week or so. Write down the building or tree or other landmark the sun touches as it sets. Do the same thing in August and each month until December. Each day the sun will slowly set further and further to the left.
I attempted to illustrate all of this using the image below. The orange lines represent the position of the sunrise and sunset on the first day of summer. The sun must travel around about three-quarters of the circle during the course of the day. In the winter the sun takes a much shorter journey only crossing just over a quarter of the sky. This is why unless you have windows which face south, much of your house will be void of sunlight in the winter months.
The speed at which the light decreases is quite slow the rest of the month, but does increase at a faster and faster pace in July. On July 1st we have lost only 36 seconds of light from the previous day. By the end of the month the lost is over 2 minutes day to day and by Labor Day the decrease is nearly 3 minutes.
Of course, this happens every year and has been happening for millions of years. The rhythm of the seasons is unaffected by humans and is one of those inexorable parts of the bigger cosmic picture that reminds me all of this is much bigger than any of us.