Spot on Blue - now we're getting somewhere. I'm being ridiculed in the pub by my claim that the Tropics move up and down; and your mention of a 41,000 year wobble cycle suggests I'm right. But this cycle is completely new to me. Is it some sort of Masonic secret? Tell us more. What causes it? At what latitude are the tropics at the extremes of this wobble? What difference is there in daylight time, at 50 North say, at the Summer Solstice?