Astronomy

Astronomical Explanation of the Summer Solstice



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Summer solstice is ridden with old folklore, customs, and traditions; it marks the first day of summer in the northern hemisphere, but in the ancient calendar, solstice was in the middle of the calendar and was surrounded by summer. Shakespeare wrote Midsummer Night's Dream inspired by the traditions of summer solstice.

Summer solstice starts the season of summer and is the longest day of the year. In 2008, summer solstice appeared on June 20, at 7:59 PM or 23:59 Universal Time. Sol sistere, the Latin word from which solstice is taken means "sun stand still." On the day of summer solstice the earth is at its maximum tilt toward the sun and it appears to stand still.

The proximity of the sun to earth has no bearing on the seasons; in fact the earth is closer to the sun in January than it is in the summer. The seasons are related directly to the rotational tilt of the earth relative to the sun.

Imagine the equator tilting 23.5 degrees toward the sun, and you have a good picture of the beginning of the summer season in the northern hemisphere. If you lived on the other side of the equator, in the southern hemisphere, you would be starting the winter season.

In the northern and southern hemispheres we see seasonal changes as a result of the earth's tilt in relation to the sun. When one hemisphere is tilting toward the sun, the other is tilting away for a reversal of seasons. The equator gets a constant amount of sunshine, but the North Pole gets several weeks of sunshine before and after the summer solstice. The sun doesn't set.

As the earth makes its circuit around the sun on it's 23.5 degrees axis, it is tilting toward the sun in the summer and away from the earth in the winter; we call these two extremes summer solstice and winter solstice. At other times on the equatorial plane, we have equal sunshine and darkness on the earth and we call these the vernal equinox and the autumnal equinox.

Astronomers have used a mathematical equation to track the solstices and equinox and with the equation can predict when they will occur each year within an hour.

Today we have satellites that orbit the earth and have access to photos beamed down to earth to give us a greater understanding of how the earth tilts and its rotation around the sun, but astronomers figured this rotational tilt out long ago using what we now would consider, crude tools.

Science is a wonder and gives us great insight to the world around us and the world above. The next time you're freezing in the cold, just remember the sun is actually closer to the earth than it was last summer. Comforting thought, isn't it?

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More about this author: Mona Gallagher

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