The earth take close to 365 1/4 days to make one revolution around the sun, but the calendar only marks out full days. So four complete revolutions take 4 * 365 1/4 = 1461 days, but the calendar records a complete year in 4*365 = 1460 days. So every four years, the calendar records January 1 another day earlier. In 100 or so of these four-year periods, January 1 is in the summer (long days, sho