Evaluating the Equation of Time

ANALEMMA is a MATLAB program which evaluates the equation of time.

The program computes and plots the equation of time, the declination, and an analemma curve for various orbital parameters. The analemma is the curve traced by the position of the sun, measured at clock noon, over a year.


analemma ( ecc, lon, obliq )
where the optional input parameters are:

The program with no options uses the following default values:


The computer code and data files described and made available on this web page are distributed under the GNU LGPL license.


ANALEMMA is available in a C version and a C++ version and a FORTRAN77 version and a FORTRAN90 version and a MATLAB version.

Related Data and Programs:

CALENDAR_RD, a C++ program which computes the representation of a given date in a number of calendrical systems, by Edward Reingold, Nachum Dershowitz.

CALPAK, a MATLAB library which makes various calendar calculations;

DATES, a dataset directory which contains lists of dates in various calendar systems.

WEEKDAY, a MATLAB library which determines the day of the week corresponding to a given date, such as 14 October 1066, Julian calendar, ... which was a Saturday.


  1. Brian Tung,
    Figure Eight in the Sky, a new perspective on an old fascination,
    Astronomical Games, August 2002,

Source Code:

Examples and Tests:

List of Routines:

You can go up one level to the MATLAB source codes.

Last revised on 05 January 2013.