* For the current year, the average day length and total yearly difference are predictions the shortest and longest day lengths are for the year so far (up to and including today). The table below shows the yearly average day lengths since 1973. So far, there have been 27 leap seconds, and they have all been positive. The system of leap seconds was introduced in 1972. A positive leap second adds a second to our clocks, while a negative leap second subtracts a second. Leap seconds can be positive or negative. When this happens, a leap second is used to bring them back into alignment. However, over the course of months and years, these small differences can add up and put our clocks out of sync with the Earth's spin. Overall, the Earth is a good timekeeper: the length of a day is consistently within a few milliseconds of 86,400 seconds, which is equivalent to 24 hours. The shortest and longest day lengths are for the year so far (up to and including today). * The figures for today and tomorrow are predictions. If every day were as long as today, a leap second would have to be added every 1349.89 days. Over this period, 21 days have been longer than today, while 345 have been shorter than today. On average, a mean solar day in the last 365 days was -0.08 ms under 24 hours, so today's day length is above average. This is the time it takes Earth to rotate 34.45 cm (13.56 in), as measured at the equator. Today is predicted to be 0.7408 ms (milliseconds) or 0.0007408 seconds longer than 24 hours. Recently, our planet has been speeding up a little, making for slightly shorter days. Within this general trend, however, there is fluctuation: sometimes the Earth spins a bit faster, sometimes a bit slower. Over the course of a century, the length of a day increases by a couple of milliseconds (where 1 millisecond equals 0.001 seconds). The Moon is-very gradually-slowing the Earth's rotation because of friction produced by tides. The Earth's rotation is not constant, so in terms of solar time, most days are a little longer or shorter than that. Modern timekeeping defines a day as the sum of 24 hours-but that is not entirely correct. ©/nukleerkedi Earth's Rotation Defines Length of Day The Earth's rotation slows down over time. Business Date to Date (exclude holidays).
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