Re:How rare is this then?

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Posted by Steve Holmes2 at 16:04 on 2011 Mar 14

Nice work Graham. Calculation trumps logic every time, I fear! I had also done a bit more work on this (manually, not using detailed calculation) and had already found the Nov 2002 and Apr 2041 events. I was only really looking for alignments in the evening sky so I would not have found some of the cases you did anyway.This work showed that the 780day synodic period of Mars was as important as the almost 20yr conjunction period of Jupiter/Saturn. This can be seen in your events in 811, 813 and 815 and other 2yr-apart pairings. I also found I had underestimated the role of Uranus: in a 40yr period it moves quite a lot! I think this is probably what accounts for the large gap between 2041 and 2154: the outer giants are simply not close enough together then to allow the others to fit into the bit of the sky that’s left. The pairs of events a couple of months apart seem to be due to the rapid motion of Mercury, re-appearing to the appropriate side of the sun before Venus has had time to move out of alignment.Your work does show though that my hunch that such alignments are not all that rare seems to be true, particularly if one further restricts oneself to the five major planets. Pity the next one isn’t until 2041 though!As to "morsels" more generally, you might have noticed that I posed an almost exactly similar question myself on the forum some time ago (with no replies at all!!). As I said at the time, I have set up a section of my personal website as a "Theory" section, in which I have placed a number of articles in the style of Jean Meeus’ books. It can be found at http://www.steveholmes.net/astro-theory. Some of the articles are very (very!) long but if you think they might survive the journey to the BAA Computing site then I would be honoured to port them across.