Astronomy

Astronomical Explanation of the Summer Solstice



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The summer solstice, also referred to as the first day of summer and the longest day of the year, occurs in the northern hemisphere on June 21 and in the southern hemisphere six months later. The summer solstice is proceeded by the spring equinox and followed by the autumn equinox. In some cultures the solstices and equinoxes were regarded as the start of their respective seasons however, for other the marked the mid-point. For this reason the summer solstice has also been referred to as midsummer's day.

Remember when you were little and your mother made you stand up straight? Luckily, our planet doesn't have to stand straight as it revolves around the sun but instead gets to lean to one side. It is this tilt, about 23.5 degrees off plum, which makes the season's possible. The tilt varies, as the Earth isn't just leaning but wobbling as well. Whether it is summer or winter where you live depends on whether the part of the earth you live on is tilted toward or away from the sun. In the northern hemisphere is tilted toward the sun between around March 20 and September 22, and on or about June 21, the earth's axis is pointed most directly at the sun.

What is the axis, you ask. The earth's axis is an imaginary line going through the earth from the South Pole and out the North Pole. For viewers north of the equator, the sun appear higher in the sky on the day of June 21st then on any other in the year. It is also the longest day of year, how long depends on how far north you live. If you live in the extreme north, say the Arctic Circle, there will be a few days when the sun doesn't even bother to go down. The closer you live to the equator the length of day is changed by the solstice.

Many ancient civilizations went to a lot of trouble to calculate when the solstices would occur; marking time by the phases of the moon was easier but not very reliable when trying to predict when to plant crops or how much of winter was left, for that you needed a solar calendar. To ancient people the sun rising later and setting earlier coupled with the advancing cold temperatures was a serious matter and the knowledge of when the days would lengthen was certainly a comfort in their harsh lives.


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