High-Precision Heliocentric Earth Orbit Computation

Dates and Math

Version Compatibility: Visual Basic 5

More information:
This is an implementation of the VSOP87 theory of planetary orbits as outlined in NASA documentation. I decided to make these modules in Visual BASIC to make such computations available on a Windows platform. Prior to this, the only other time I saw a complete, equal treatment of the subject, the language used was FORTRAN. Since VB is becoming very popular, it's about time the VSOP87 theory was implemented in that language too, so more amateurs can try their hand at making astronomical programs in a language that is much easier to work with and reasonably simple to understand.

This module handles the orbit of the Earth, however modules are being developed to compute the orbits of the planets Mercury to Neptune, also according to the VSOP87 theory of orbital dynamics.

These modules are not for the mathematically squeamish!. They involve a significant understanding of astro-mathematics to grasp just what the computations are about, but the program does at least take the worst part of the labor out of the process of computing planetary positions from a heliocentric viewpoint.

The modules come with a demonstration interface that allows the user to enter any given date and time for which to perform the computations and get a feel for what the modules do. All the user does is enter a date and time and the program does the rest.

The computed heliocentric, spherical coordinates are: L = Longitude
B = Latitude
R = Radius vector (= Distance between Sun and Earth)

The function modules perform many thousands of complex computations taking into account such things as precession, planetary perturbations and the orbital effects of relativity over the long-term. As a result, the heliocentric accuracy is to about 1 arc second or better over the time period from 2000 BC to 6000 AD. The computations refer to the mean ecliptic and equinox of the given date for which the computations are performed.

Instructions: Click the link below to download the code. Select 'Save' from the IE popup dialog. Once downloaded, open the .zip file from your local drive using WinZip or a comparable program to view the contents.

Download earth.zip