ALT-1 Astronomy the Summer Solstice Explained
The earth in its orbit around the sun neither follows a circular path, nor does that orbit fall consistently on the plane of the equator. This second fact gives rise to the possibility, and the cause, of both solstices and equinoxes.
The shape of the earth's orbit, which is an ellipse, has little bearing on the solstice. The tilt of the earth, though, is directly related to the solstices and the equinoxes.
To understand this, it is important to know that the tilt of this planet is inclined by approximately 23.5 degrees. During the summer in the Northern Hemisphere, this means that the hemisphere is tilted more directly toward the sun. The opposite is true in the Southern Hemisphere at the same time of year, so when it is summertime in the northern half of our world, it is wintertime in the southern half.
The tilt causes two things that can be noticed by nearly everyone not living at the equator, though they are more pronounced the further north or south latitude that the observer happens to be. On the equator, the change is so minor that it is more difficult to detect.
One of the noticeable things is that the number of hours in the day, as compared to the number of hours in the night, increases as a hemisphere progressively moves to the point it is most directly facing the sun. At that point, which is the summer solstice, the days begin to shorten again until the tilt has moved the hemisphere so it is pointing as far away from the sun as it will get in its orbit. This is the winter solstice. In other words, the longest day occurs at summer solstice and the shortest day occurs at winter solstice.
This is also why, in the Arctic Circle, during summer solstice the sun doesn't appear to ever completely set, but during the winter solstice it never seems to totally rise.
What is also noticeable is that in the Northern Hemisphere, as the earth passes beyond the winter solstice, the point on the horizon where the sun appears to rise begins a northerly trek. Each day, the sun will appear to rise a little further north than it did the day before. At the summer solstice, it will look like it has risen at its most northerly point. It will then seem to start setting progressively further south until winter solstice.
It should also be pointed out that due to the earth's tilt, at summer solstice the sun's rays are striking the earth the most directly. This is also what creates the seasons. However the earth doesn't warm up immediately or quickly, which is why the coldest temperatures are usually recorded somewhat after the winter solstice, and the hottest temperatures generally occur a month or two after summer solstice.
Even ancient civilizations had the ability to work out the solstices, and many even had a good idea of what caused them. In the modern day, mathematics is used to figure out the dates and times of the solstices with great precision. However, simple observation will usually be very close.
For many reasons, the solstices have had a profound affect on mankind. However it isn't difficult to figure out the cause, nor when they will occur. They are cycles that have been recorded for thousands of years, perhaps longer.
