Utc clock for computer5/15/2023 During a positive leap second at the end of a day, which occurs about every year and a half on average, the Unix time number increases continuously into the next day during the leap second and then at the end of the leap second jumps back by 1 (returning to the start of the next day). No negative leap second has ever been declared, but if one were to be, then at the end of a day with a negative leap second, the Unix time number would jump up by 1 to the start of the next day. Leap seconds may be positive or negative. When a leap second occurs, the UTC day is not exactly 86 400 seconds long and the Unix time number (which always increases by exactly 86 400 each day) experiences a discontinuity. Unix time across midnight into 17 September 2004 (no leap second) ![]() For example, at the end of the day used in the examples above, the time representations progress as follows: The above scheme means that on a normal UTC day, which has a duration of 86 400 seconds, the Unix time number changes in a continuous manner across midnight. Sometimes, Unix time is mistakenly referred to as Epoch time, because Unix time is based on an epoch and because of a common misunderstanding that the Unix epoch is the only epoch (often called " the Epoch" ). This applies within days as well the time number at any given time of a day is the number of seconds that has passed since the midnight starting that day added to the time number of that midnight. This can be extended backwards from the epoch too, using negative numbers thus, 4472 days before the epoch, is represented by the Unix time number −4472 × 86 400 = −386 380 800. Thus, 12 677 days after the epoch, is represented by the Unix time number 12 677 × 86 400 = 1 095 292 800. The Unix time number is zero at the Unix epoch and increases by exactly 86 400 per day since the epoch. For brevity, the remainder of this section uses ISO 8601 date and time format, in which the Unix epoch is. There is a problem with this definition, in that UTC did not exist in its current form until 1972 this issue is discussed below. The Unix epoch is the time 00:00:00 UTC on 1 January 1970. Interpreter programs can then convert it to a human-readable format. Unix time is a single signed number that increments every second, which makes it easier for computers to store and manipulate than conventional date systems. Each leap second uses the timestamp of a second that immediately precedes or follows it. In Unix time, every day contains exactly 86 400 seconds but leap seconds are accounted for. International Atomic Time (TAI), in which every day is precisely 86 400 seconds long, ignores solar time and gradually loses synchronization with the Earth's rotation at a rate of roughly one second per year. UTC includes leap seconds that adjust for the discrepancy between precise time, as measured by atomic clocks, and solar time, relating to the position of the earth in relation to the sun. Unix time differs from both Coordinated Universal Time (UTC) and International Atomic Time (TAI) in its handling of leap seconds. The second layer encodes that number as a sequence of bits or decimal digits. The first layer encodes a point in time as a scalar real number which represents the number of seconds that have passed since 00:00:00 UTC on Thursday, 1 January 1970. ![]() ![]() Two layers of encoding make up Unix time. It has come to be widely used in other computer operating systems, file systems, programming languages, and databases. Unix time originated as the system time of Unix operating systems. It measures time by the number of seconds that have elapsed since 00:00:00 UTC on 1 January 1970, the beginning of the Unix epoch, less adjustments made due to leap seconds. Unix time is a date and time representation widely used in computing. It was celebrated in Copenhagen, Denmark at a party held by the Danish UNIX User Group at 03:46:40 local time. Unix time passed 1 000 000 000 seconds on.
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