Earth's Day is less than the solar day. In the period 1 on the sun and a star on two heads. Period 2 is the 360 ° rotation of the Earth, the star is above the head but not the Sun (1 → 2 = a star day). At sunset 3 the sun is on top of the head (1 → 3 = one solar day)
Main article: Mean solar time
In a year, the average solar day's average is known as average solar day. Average solar day is made of 86,400 average solar seconds. This sec is far longer than the standard second. Since the year 1972, average solar day is 0-2 milliseconds longer than 86,400 standard seconds.
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