The analemma shows a relationship between the sun's declination and the difference between sun time and mean time. This relationship is of importance in designing a sundial that is to read mean sun time or clock time.

C language computer program to calculate the analemma using two different methods. Analemma Calculation

Analemma data generated by the above calculation. Analemma Data

Analemma data projected onto a sphere as seen from the outside of the sphere.

Analemma data projected with arrows showing seasonal motion of the sun.

C language program that calculates the analemma and projects the result onto a user defined plane surface. These projections are the markings that are found on a sundial of the type indicated. Analemma Projection

Results of the analemma projections onto plane surfaces at various places on the earth. Notation (the name on the image) is type.del.dec where del is the offset of the users meridian from the noon meridian and dec is the users declination. Various Sundial Markings

 

Photo of the Analemma (as seen from the surface of the earth and as seen over a year long time period.)
Courtesy of the photographer, Dennis di Cicco and "Sky & Telescope" magazine.