Sunday, June 17, 2007

Solar Analemma

As well-known by simple observation, in Summer the Sun rises near the North-East and in Winter it rises near the South-East. Besides, the apparent height of the Sun in the sky is always lower in Winter than in Summer. With these premises, what would happen if we take a picture of the Sun everyday at the same time? The result would be a figure called analemma.

The shape is different if the pictures are taken at different lattitudes and at different times. Check how the inclination of the analemma changes when it is obtained at different times in this website.

The characteristic 8-shaped figure is determined by the inclination of the Earth rotation axis with respect to the movement plane around the Sun as well as the eccentricity of the elliptical orbit around the Sun. If so, it is easy to understand that in other planets the analemma must be differently shaped. For example, in Mars it is teardrop-like.

Other celestial bodies can also follow nice analemmas on the sky. For example the Moon. This case is quite nice since the different lunar phases are also visible in the diagram.

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