Most recent change of Analemma
Edit made on July 07, 2011 by PhilRamsden at 22:08:02
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Suppose that a camera is permanently fixed and a photograph of the Sun is taken at the same time (say noon) on each day for a complete year.
The resulting curve traced out is called the Earth's Analemma of the Sun.
Two things affect a planet's analemma: the eccentricity of the orbit (which causes an annual oscillation) and the tilt of the planet (which causes a biannual one). For the Earth, the latter is dominant, meaning that the Earth's analemma is figure-of-eight shaped. Mars, whose orbit is much more eccentric, has a teardrop-shaped analemma.