Transits:Why and When?
We have seen that if we draw a plan of the Solar System on a flat piece of paper, we are not very far wrong; but the slight inclinations of the orbits of Mercury and Venus make all the difference insofar as transits are concerned. If their orbits were in the same plane as ours, the planet would transit at every inferior conjunction — that is to say every 116 days for Mercury and every 584 days for Venus. In fact this does not happen, and transits are comparatively rare.
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