Today’s post is in celebration of the summer solstice and all things solsticey.
If someone asked you to define a year, what would you say? Probably a lot of people would opt for “the length of time it takes the earth to go round the sun”. If asked to be more precise, these people might suggest the interval between successive alignments of the sun and a particular star, where hopefully that star would be chosen so as to have a small proper motion – in other words, as near as dammit a “fixed” star.
But if we did define a year in such a way, over a long period of time we would notice something rather odd happening. Summer (and indeed all the seasons) would come slightly earlier each year; after two thousand years, midsummer would be a whole month earlier, and after just under 13,000 years midsummer would be in December. Continue reading