Monday, June 21, 2010

Summer Solstice Plus 6

At this writing we are very nearly 6 hours past summer solstice. In southeast Texas summer solstice occurred early this morning at 6:28 AM CDT.

What is summer solstice and why should we care?

Summer solstice is the longest day of the year. The sun will stay above the horizon for the longest total elapsed time, here in the northern hemisphere, than any other day of the year.

This is because Earth rotates on its axis at a 23.44 degree angle to the plane that contains the elliptical orbit that Earth takes around the Sun. So this morning, Earth, in its elliptical orbit around the Sun is nearing its furthest distance, or aphelion, from the Sun. But in being at this extreme, the Earth’s northern hemisphere is tilted toward the Sun to its fullest extent. Rays from the sun are incident on Earth’s northern hemisphere at the highest, that is, least oblique angle.

Earth receives the Sun’s rays with less filtering by the atmosphere in the northern hemisphere than in the southern hemisphere. It is therefore summer here in the northern half of Earth, and winter in the southern half.

Winter temperatures in the northern hemisphere are milder than those in the southern hemisphere but how much that has to do with Earth’s tilt is unknown because on Earth, most of the landmass occurs in the northern hemisphere and land, in general, is warmer than the oceans.

On Earth, the Sun will appear to set on the horizon as far to the north as it does set. From now, until December 21st, the sun will set continually further and further south.

Living in the northern hemisphere is a little different than living on the equator. I did that for about 5 years. On the equator, the sun sets at exactly the same time every day. It rises at the same time as well. And when the sun sets, darkness comes quickly. Here in the northern hemisphere, we have twilight. Twilight extends for a longer period of time as the days grow longer.

What does all of this have to do with politics, the BP oil spill or the War in Afghanistan?

Not a blasted thing as far as I can tell.

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