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Paul's Puzzle Number Three

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Grand Alignment

It had been an arduous mission, so as I left the Centurion Eagle in the space park, I was looking forward to long, cool Bellatrix Stinger. As I entered I spotted Darth Vader's younger (and much more personable) brother, Spacin, sitting in the corner.

'Hey, Singleton,' he shouted, 'come and join me for a drink.' I walked over and a little green creature followed with my Stinger. 'How's things, Spacin?' I enquired.

'I've just returned from the Grand Alignment celebrations on my home planet. That doesn't happen very often, you know.'

'Tell me more,' I said.

'Well, there are three planets in our solar system. Their orbits have very low eccentricity and they all lie in a plane.'

'You mean their orbits a nearly circular?' I asked.

'Quite so,' replied Spacin. 'Furthermore the outer planet goes around the Sun every sixty years, the middle planet has a period of 20 years, and my home planet has a period of just 12 years.'

'I see. So the next Grand Alignment will be in 60 years?'

'Singleton,' he said, 'You're a great fighter pilot, but if I was you, I'd leave the calculations to the onboard computer.'

How often are the Sun and planets aligned ?

(This puzzle is now closed!)

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