ANALEMMA Evaluating the Equation of Time

ANALEMMA is a C program which evaluates the equation of time, by Brian Tung.

The program can compute and plot 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.

The program creates data and command files which must be processed by the GNUPLOT program:

```        gnuplot < analemma_commands.txt
```
which will create PNG images of the analemma, the declination, and the equation of time.

Usage:

analemma options
where the allowable options include
• -e ecc, the eccentricity;
• -l lon, the perihelion longitude in degrees;
• -o obliq, the axial obliquity in degrees;
• -h ecc, print the usage information;

The program with no options uses the following default values:

• eccentricity = 0.01671;
• longitude of perihelion = 1.347 radians = 77.18 degrees;
• axial obliquity = 0.4091 radians = 23.44 degrees;

Languages:

ANALEMMA is available in a C version and a C++ version and a FORTRAN90 version and a MATLAB version and a Python 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 C++ library which makes various calendar calculations;

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

GNUPLOT, examples which illustrate the use of the gnuplot graphics program.

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

Author:

Original C version by Brian Tung. This C version by John Burkardt.

Reference:

1. Brian Tung,
Figure Eight in the Sky, a new perspective on an old fascination,
Astronomical Games, August 2002,
http://www.astronomycorner.net/games/analemma.html.

Source Code:

Last revised on 24 October 2018.