![]() Some proposals have been made to implement larger corrections like leap hours, which would occur much less often than leap seconds. Special attention must be given to these systems each time there is a leap second. However, adding a second to UTC can create problems for some systems, including data logging applications, telecommunication systems and time distribution services. If there were no longer a correction to UTC for leap seconds, then adjustments would have to be made to time stamps and legacy equipment and software which synchronize to UTC for astronomical observations. The designation of the sequence to remove a second would be:Īre there benefits and/or detriments to adding leap seconds?īy keeping Coordinated Universal Time (UTC) within one second of astronomical time, scientists and astronomers observing celestial bodies can use UTC for most purposes. However, there is a provision for negative leap seconds if it becomes necessary due to changes in Earth's rotation. So far, there have only been positive leap seconds. The designation of the sequence of seconds is:Ġ0h 00m 00s (the beginning of the following date) Leap seconds have always occurred at the end of December or the end of June, on the last second of the UTC day. The current difference between UTC and UT1 is shown in our leap second archive web page. At the time the corrections started in 1972, a necessary correction of ten seconds was made to UTC, and there have been leap seconds about every year and a half (on average). Usually leap seconds are added when UTC is ahead of UT1 by 0.4 seconds or more. The International Earth Rotation and Reference Systems Service (IERS), measures Earth's rotation and publishes the difference between UT1 and UTC. ![]() Leap seconds are added in order to keep the difference between UTC and astronomical time (UT1) to less than 0.9 seconds. This gradual decrease in the rotational rate is causing the duration of the mean solar second to gradually increase with respect to the atomic second.įor information about past leap seconds and the measured differences between UTC and UT1, please see the NIST Time Scale Data Archive. It sometimes speeds up, and sometimes slows down, but when averaged over long intervals the trend indicates that it is gradually slowing. The second reason for leap seconds is that the speed of the Earth's rotation is not constant. If the atomic second had been defined with respect to the mean solar second, it is likely that leap seconds would have been required much less frequently. The duration of the ephemeris second was slightly shorter than the mean solar second and this characteristic was passed along to the atomic second. The first is that the duration of the atomic second was measured and defined by comparing cesium clocks to the Ephemeris Time (ET) scale, an obsolete time scale that defined the second as a fraction of the tropical year. There are two main reasons that cause leap seconds to occur. Astronomical time (UT1), or mean solar time, is based on the rotation of Earth, which is irregular. UTC is an atomic time scale, based on the performance of atomic clocks that are more stable than the Earth's rotational rate. How is a leap second related to a leap year?Ī leap second is a second added to Coordinated Universal Time (UTC) in order to keep it synchronized with astronomical time. ![]() Are there benefits and/or detriments to adding leap seconds?.What leap seconds are, how they are implemented and their future.
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