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Saturday, November 27, 2004

Quarter Million Year Canon of Solar System Transits

Last May I decided to see if the long-term evolution of planetary orbits in the Solar System ever resulted in a simultaneous transit of Mercury and Venus visible from Earth in the distant past or future (I chose a period of ±125,000 years for the investigation). Little did I know at the time that Jean Meeus was working on the same problem, and beat me to the solution, publishing the July 69163 simultaneous transit in the June 2004 issue of The Journal of the British Astronomical Association. But all was not lost, since my transit finder, based on Steve Moshier's DE118i-2 numerical integrator, was producing a list of all planetary transits (excluding grazes and short events which start and end within one integration step of 1/100 day [14.4 minutes]), plus barycentre excursions. Suitably post-processed by a camel of Perl programs, the results were assembled into a comprehensive catalogue of transits, which is now posted. All of the software used to produce the canon is available for downloading, as is the canon itself in CSV format. Computation of the list of transits took two months on my 1 GHz "laptop", with the backward integration running for a month in parallel on another 400 MHz machine, then transferred back to the faster laptop after it completed the forward integration. In any project like this, one always worries about whether the answers obtained are, you know, right, so I spent a lot of time on both internal consistency checks of the results and comparing them to other published investigations of historical and future transits, described in a section near the end of the document.

Posted at November 27, 2004 15:45