So we’re interested in Regulus and its conjunctions with the planets, and especially in triple conjunctions with Regulus. How often do these occur? Are they a rare thing?
No, triple conjunctions aren’t particularly rare, though they are less common and thus more interesting than ordinary single conjunctions. Let’s look at the patterns of the planets’ conjunctions with Regulus and see how often they occur. In general they happen more frequently for the planets which are closer to the Sun and thus take less time for their journey around it.
What we’re most interested in here is visible conjunctions, those which an observer on earth could see without the aid of a telescope. This means conjunctions with any of the first five planets. The unseen planets Uranus, Neptune, and Pluto will also be found to be relevant, but serving a different kind of purpose. Rather than producing their own visible conjunctions, their presence influences the paths of the visible planets, providing some fine tuning of precisely when and where the visible conjunctions will occur.
Of the visible planets, we’ll start with the one farthest from the Sun – Saturn, the one which takes the longest time for its orbit. Click on the following links to see data on the cycles of Saturn and the other planets:
The orbital periods of the planets are found at http://solarsystem.nasa.gov/planetinfo/charchart.cfm for all but Pluto, and Pluto’s orbital period can be found at http://solarsystem.nasa.gov/planets/compare?Object1=neptune&Object2=pluto. Here’s the complete list as compiled from these sources –
Orbital periods of the planets:
Mercury – 0.2408467 year
Venus – 0.61519726 year
Earth – 1.0000174 year
Mars – 1.8808476 years
Jupiter – 11.862615 years
Saturn – 29.447498 years
Uranus – 84.016846 years
Neptune – 164.79132 years
Pluto – 247.92065 years