Analemma

Definitions

  • Webster's Revised Unabridged Dictionary
    • Analemma A scale of the sun's declination for each day of the year, drawn across the torrid zone on an artificial terrestrial globe.
    • Analemma 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.
    • Analemma (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.
    • ***
Century Dictionary and Cyclopedia
    • n analemma A form of sun-dial, now disused.
    • n analemma In geometry, an orthographic projection of the sphere on the plane of the meridian, the eye being supposed to be at an infinite distance, and in the east or west point of the horizon.
    • n analemma Hence An instrument of wood or brass on which a projection of this nature is drawn, formerly used in solving astronomical problems.
    • n analemma A tabu-lated scale, usually drawn in the form of the figure 8, depicted across the torrid zone on a terrestrial globe, to show the sun's declination and the equation of time on any day of the year.
    • ***

Etymology

Webster's Revised Unabridged Dictionary
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

Usage


In news:

Analemma Society hosts lecture, fundraiser for sundial replica.
A design of the sundial at the mosque in Damascus, which the Analemma Society hopes to fund a replica for Observatory Park at Turner Farm.
***

In science:

Finally, we illustrate the concepts of the “equation of time” and the analemma.
The sun's position in the sky
III A).18 The equation of time can be read from the horizontal displacement of the analemma in Fig. 16(c).
The sun's position in the sky
In that plot, each degree of azimuthal displacement away from ϕ(cid:12) = 180◦ translates to 24 hours /360 = 4 minutes in the equation of time for that date. A convenient check of the validity of our computations is to compare this analemma with the one available at , based on data from .
The sun's position in the sky
Even though the position of the sun in the sky for a given hour, calendar date, and location, is not quite constant from one year to the next, the way in which the mean solar time is defined ensures that the shape of the analemma remains unchanged.
The sun's position in the sky
The word “analemma” derives from the Greek term for the pedestal of a sundial and refers to the instructions on how to correct a sundial’s reading for the equation of time, which can give an adjustment of as much as a quarter of an hour.
The sun's position in the sky
Introductory textbooks and other pedagogical sources sometimes explain the analemma’s horizontal displacement as resulting solely or primarily from the eccentricity of the earth’s orbit (see, e.g., ).
The sun's position in the sky
If this were the dominant factor in determining the equation of time, then the azimuth of the sun, observed at noon, would be greater than 180◦ during half of the year and smaller than 180◦ during the other half, giving a figure 0 rather than a figure 8 for the analemma.
The sun's position in the sky
Orbital eccentricity does play an important role in determining the precise form of the equation of time, but the analemma would still be a figure 8 if the earth’s orbit were perfectly circular.
The sun's position in the sky
This motion is similar to the effect of the inclination of the ecliptic on the equation of time that can be seen in an analemma.
COBE Tutorial and Recent Results
***