By Daniel Brown in The Conversation.
Most of the time, a year is made up of 365 days. But this year, just like 2012, and the year four years before that, has 366. And that vital extra day, a leap day, is (partly) what keeps our calendars in working order.
As users of a solar calendar, we rely on the sun to tell us how long a year is and when each of the four seasons begins. It was devised to match our farming habits and as a reliable – and visible – guide to the passing of time. The sun’s position on the horizon as it rises and sets moves over the course of a year, further south in the winter, and further north in the summer. This significant change is used to mark midwinter or midsummer at famous locations such as Stonehenge and New Grange.
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