Gregorian calendar

First, the Julian calendar had no complaints, but gradually found that year lasts for 11 minutes less, than counted. This error was corrected in 1582 by Pope Gregory XIII, who decreed the day 5 October 15 Oct. Otherwise the calendar date more and more would not coincide with certain seasons. To exclude such error in the future, he also gave the order century years (at the turn of the century) to be leap-year only when they are divided by 400 without a remainder. This Gregorian calendar is still used in Western countries.
Night and day was the shortest periods of time known to our ancestors. A more accurate calculation of time appeared about 4000 p. n. e., when ancient Egyptians divided the time of day on the clock. The first timepiece was the sundial, consisting mainly of the column which is stuck into the ground so that it cast a shadow on the dial with hour divisions. When the sun moved across the sky, the shadow of the column moved on a scale and showed time.