Analemma: Encyclopedia II - Analemma - Explanation

Analemma - Explanation

Due to the earth's tilt on its axis (23.45°) and its elliptical orbit around the sun, the relative location of the sun above the horizon is not constant from day to day when observed at the same time on each day. Depending on one's geographical latitude, this loop will be inclined at different angles.

The vertical coordinate of a point corresponding to a date corresponds to the declination of the sun on that date, while the horizontal coordinate indicates whether the sun is "fast" or "slow" compared to mean time as measured by clocks.

The deviation between solar time and mean time is known as the equation of time and is due to the variation in the length of the synodic day, which is due to variation in the distance between the earth and the sun. (See aphelion, perihelion.)

Plotting the analemma with the width exaggerated shows that it is slightly asymmetrical due to the misalignment of apsides and solstices.

Adapted from the Wikipedia article "Explanation", under the G.N U Free Docmentation License. Please also see http://en.wikipedia.org/wiki