Summer Solstice

StarDate: June 21, 2011

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Here in Texas, where we've already had record high temperatures and record wildfires this year, it's not the most welcome of news, but here goes anyway: Summer arrives today in the northern hemisphere. It begins at 12:16 p.m. Central Daylight Time -- the moment of the June solstice. It's the longest day of the year, and the day the Sun stands farthest north in the sky.

"Solstice" means "Sun stands still." It refers to the Sun's position along the horizon as it rises and sets.

From the latitudes of the United States, the Sun makes a wide arc along the eastern and western horizons over the course of a year. And for much of the year, you can see that motion from day to day. If you were to watch the sunrise or sunset from the same spot each day, and compare the Sun's position relative to landmarks on the horizon, you'd see the Sun scooching northward or southward from one day to the next.

Around the solstices, though, it slows down and then stops. So for several days, it rises and sets at the same spots along the horizon.

All of that motion is the result of Earth's tilt on its axis. As Earth orbits the Sun, our viewing angle changes from day to day, causing the Sun to move north and south. At the June solstice, the north pole tips most directly toward the Sun. And at the December solstice, the south pole nods that way -- providing cooler weather in the northern hemisphere -- including, we hope, right here in Texas.

 

Script by Damond Benningfield, Copyright 2011

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