Signs and Seasons, Days and Years

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Solex

Solex1To search for all occurrences of a particular kind of conjunction in a particular time period, a powerful little program called Solex is available at http://www.solexorb.it/SolexOld/. This too is available for free. If you’re interested in an expanded range of years, allowing exploration much deeper into the past, the author of the program makes this available for no charge as well, if you just follow his instructions for program registration.

The name Solex comes from “Solar system integration by a fast extrapolation method”, and its heart is a powerful numerical integrator, computing the positions of solar system bodies by numerical integration of the Newton equation of motion. Given the position and velocity of each body at a known starting point, the accelerations arising from the mutual gravitational forces are computed; from this the new positions and velocities after a short time interval are determined; and then this process is repeated over and over in order to identify the positions of the bodies at any desired end point.

Solex is a very precise ephemeris generator. Its precision is comparable to that of the JPL Horizons system, and exceeds the precision achievable by ordinary planetarium programs like Stellarium and Starry Night. For present-day modeling of the Solar System and even for dates as far back as 1000 BC, the results of ordinary planetarium programs do often match the results of Solex quite well. But for ancient dates of 3000 BC and older the precision of ordinary Planetarium programs tends to begin falling away, with the results of Solex being noticeably more reliable.


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