Solar Tracking

There is a pattern that the sun follows every year.It might seem that the Sun traces out a circle when it orbits the Earth, which is actually a misconception. If you were to go outside and look at the sky at a specific time once a day for an entire year, you'd notice that the sun changes its position. (see the Analemma) The path of the Earth around the sun is actual a very subtle ellipse, which is more oval than a circle. The combination of the Earth's axis being tilted and the elliptical path of the sun give rise to the spring and fall solstices and the summer and winter equinoxes.

On these days the path of the sun in the sky is uniquely different than the rest of the year. At noon on the equinoxes, the angle of the height of the sun and the horizon is exactly 90 minus the degree of latitude you are measuring from (this measurement is termed the co-latitude). On these days, the sun will rise directly in the east and set directly in the west. They also mark halfway points between the seasons of summer and winter. Another interesting fact is that on the equinoxes, the length of a day is exactly 12 hours.

After the equinoxes occur, the days will get longer or shorted, depending on which season is approaching. Due to what we've already talked about, there has to be longest and a shortest day every year. These occur on the summer and winter solstices, respectively. Use the Solar Tracker Java Tool to see for yourself how the sun changes position in the sky, depending on the Earth's placement on its orbit around the sun.

The spring and fall equinoxes take place on March 21st and September 23rd, respectively. The winter solstice happens on the same day every year, December 21st. The summer solstice occurs similarly on June 21st. These days occur like clockwork each and every year. Amazing!

Some Links on the Equinox and Solstice

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