What is an analemma?

This is what the sun looks like when you take a picture a week, for a year, always at the same time of the day, and in the same place.

This is an analemma.

Due to the 23.5° inclination of earth’s axis and the ellipticity of its orbit, the height of the sun is not the same every day, and the combined effects is what the image shows.

The height of the points corresponds to the declination of the sun on that date, while the horizontal coordinate indicates the deviation of the solar position with respect to the average time (shown by clocks).

The inclination of the figure depends on the latitude in which it is observed and on the time.

If earth’s orbit were a perfect circle and its axis were perpendicular to the orbit, the sun would be in the same spot every day and the analemma would be a point. With a circular orbit but an inclined axis, the two parts of the analemma would be symmetrical. If the axis were not inclined but the orbit were elliptical, the analemma would instead be a segment.

On other planets the analemma has a different shape, on Mars for example, it looks like a drop.