Did you know?


The tropical year, associated with the earth’s orbit around the sun, takes exactly 365.242... days, that is 365 full days and almost one fourth of the day. This additional fraction of the day causes, that despite that common year is 365 days long, to equate the calendar year with a tropical year, once every four years we have a leap year of 366 days. Very occasionally there are 61 seconds in a minute, called a leap second, applied to UTC to synchronize atomic time with solar time. Since UTC was introduced on 1 January 1972, there have been 27 leap [...]

Did you know?2019-03-21T10:50:27+00:00

History of time measurement


History of time measurement Humanity has sought to measure time for thousands of years. Natural markers of the passage of time, such as day passing into night and changing of the seasons, held huge significance throughout history but the first civilization to apply astronomical observations for measuring time was the ancient Egyptians, first using sundials clocks to divide the day into measurable parts. The division of the day and night into 12 parts probably came from the Sumerians that used the sexagesimal (base 60) system of counting from around the third millennium BC. Rather than count using all ten fingers [...]

History of time measurement2019-03-21T10:49:30+00:00

Definitions of the second


For most of its history, the second was defined as a fraction of the average solar day, based on the position of the sun in the sky. One second was exactly 1/86 400 of the average solar day. In 1956, the International Committee for Weights and Measures (CIPM) proposed new definition of the second as follows: The second is the fraction 1/31 556 925.9747 of the tropical year for 1900 January 0 at 12 hours ephemeris time This definition was formally adopted by the General Conference of Weights and Measures (CGPM) in 1960. In 1967, [...]

Definitions of the second2019-03-21T10:46:18+00:00