What is "analemma"

Analemma \An`a*lem"ma\ (-l[e^]m"m[.a]), n. [L. analemma a sun dial on a pedestal, showing the latitude and meridian of a place, Gr. 'ana`lhmma a support, or thing supported, a sun dial, fr. 'analamba`nein to take up; 'ana` + lamba`nein to take.]

1. (Chem.) An orthographic projection of the sphere on the plane of the meridian, the eye being supposed at an infinite distance, and in the east or west point of the horizon.

2. An instrument of wood or brass, on which this projection of the sphere is made, having a movable horizon or cursor; -- formerly much used in solving some common astronomical problems.

3. A scale of the sun's declination for each day of the year, drawn across the torrid zone on an artificial terrestrial globe. [1913 Webster] ||

1650s, from Latin analemma "the pedestal of a sundial," hence the sundial itself, from Greek analemma "prop, support," from analambanein "to receive, take up, restore," from ana- "up" (see ana-) + lambanein "to take," from PIE root *(s)lagw- "to seize, take" (cognates: Sanskrit labhate, rabhate "seizes;" Old English læccan "to seize, grasp;" Greek lazomai "I take, grasp;" Old Church Slavonic leca "to catch, snare;" Lithuanian lobis "possession, riches").

n. An egg-shaped or figure-eight curve that results when the Sun's position in the sky is plotted out over the year at the same hour of http://en.wikipedia.org/wiki/Solar_time every day.

In astronomy, an analemma (; from Greek analēmma "support") is a diagram showing the deviation of the Sun from its mean motion in the sky, as viewed from a fixed location on the Earth. Due to the Earth's axial tilt and orbital eccentricity, the Sun will not be in the same position in the sky at the same time every day. The north–south component of the analemma is the Sun's declination, and the east–west component is the equation of time. This diagram has the form of a slender figure-eight, and can often be found on globes of the Earth.

Diagrams of analemmas frequently carry marks that show the position of the Sun at various closely spaced dates throughout the year. Analemmas with date marks can be used for various practical purposes. Without date marks, they are of little use, except as decoration.

Analemmas (as they are known today) have been used in conjunction with sundials since the 18th century to convert between apparent and mean solar time. Prior to this, the term referred to any tool or method used in the construction of sundials.

It is possible to photograph the analemma by keeping a camera at a fixed location and orientation and taking multiple exposures throughout the year, always at the same clock-time.

Although the term "analemma" usually refers to the Earth's solar analemma, it can be applied to other celestial bodies as well.