Tag Archives: Analemma

Analemma, the Slender Figure Eight in the Sky


Myself 

By T. V. Antony Raj

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Definition of Analemma by Merriam-Webster: “A plot or graph of the position of the sun in the sky at a certain time of day (such as noon) at one locale measured throughout the year that has the shape of a figure 8; also : a scale (as on a globe or sundial) based on such a plot that shows the sun’s position for each day of the year or that allows local mean time to be determined.

Our Earth orbits around the Sun on an elliptical path. It also revolves around the Sun on a slant with an axial tilt of about 23.4 degrees. This leads to some interesting observational effects. One of these is the analemma, the apparent path traced by the Sun in the sky when observed at the same time of day over the course of a year.

Due to the Earth’s orbital eccentricity and its axial tilt, our Sun does not appear in the same position in the sky at the same time every day throughout the year. These two factors combine to generate the slender figure-eight, called analemma ( Greek “support”) curve.

So, the astronomers use this analemma diagram that shows the deviation of the Sun from its mean motion in the sky, as viewed from a fixed location on the Earth.

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Analemma on a globe (Source: analemma.com)

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The analemma diagram with the Sun’s path resembling a lopsided figure eight can often be found printed on globes of the Earth, usually somewhere over the Pacific Ocean where there is lots of room to print it.

The north–south component of the analemma is the Sun’s declination, and the east–west component is the equation of time. Most often, the diagrams of analemmas carry marks that show the position of the Sun at various closely spaced dates throughout the year. Analemmas with date marks are used for various practical purposes. Without date marks, they are of little use, except as decoration.

Earlier, prior to the 18th century, the term “analemma” referred to any tool or method used in the construction of sundials. Now, the term “analemma” is used in conjunction with sundials to convert between apparent and mean solar time.

Analemmas are photographed by keeping a camera at a fixed location and orientation and taking multiple exposures throughout the year, always at the same clock-time.

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Analemma posted by Giuseppe Donatiello

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The above image is a photo of an analemma posted by Giuseppe Donatiello.

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Analemma photo taken by Jack Fishburn in 1998–99.

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The above is an afternoon analemma photo taken in 1998–99 by Jack Fishburn in Murray Hill, New Jersey, USA. The Bell Laboratories building is in the foreground.

Although the term “analemma” is used to refer to the Earth’s solar analemma, it can be applied to other celestial bodies as well.

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