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In the International System of Units (SI), the unit of time is the second (symbol: ). It is a SI base unit, and has been defined since 1967 as "the duration of 9,192,631,770 [cycles] of the radiation corresponding to the transition between the two hyperfine levels of the ground state of the caesium 133 atom". [12]
The leap seconds cannot be predicted far in advance due to the unpredictable rate of the rotation of Earth. Nearly all UTC days contain exactly 86,400 SI seconds with exactly 60 seconds in each minute. UTC is within about one second of mean solar time (such as UT1) at 0° longitude, (at the IERS Reference Meridian).
An order of magnitude of time is usually a decimal prefix or decimal order-of-magnitude quantity together with a base unit of time, like a microsecond or a million years. In some cases, the order of magnitude may be implied (usually 1), like a "second" or "year". In other cases, the quantity name implies the base unit, like "century".
t. e. Metric time is the measure of time intervals using the metric system. The modern SI system defines the second as the base unit of time, and forms multiples and submultiples with metric prefixes such as kiloseconds and milliseconds. Other units of time – minute, hour, and day – are accepted for use with SI, but are not part of it.
A minute (min) is 60 seconds in length (or, rarely, 59 or 61 seconds when leap seconds are employed), and an hour is 60 minutes or 3600 seconds in length. A day is usually 24 hours or 86,400 seconds in length; however, the duration of a calendar day can vary due to Daylight saving time and Leap seconds .
e. In chemistry, pH ( / piːˈeɪtʃ / pee-AYCH ), also referred to as acidity or basicity, historically denotes " potential of hydrogen " (or "power of hydrogen"). [1] It is a logarithmic scale used to specify the acidity or basicity of aqueous solutions. Acidic solutions (solutions with higher concentrations of hydrogen ( H+) ions) are ...
Philippine Standard Time (PST or PhST; Filipino: Pamantayang Oras ng Pilipinas), also known as Philippine Time (PHT), [citation needed] is the official name for the time zone used in the Philippines. The country only uses a single time zone, at an offset of UTC+08:00 , but has used daylight saving time for brief periods in the 20th century ...
ISO 8601. International standard ISO 8601 ( Representation of dates and times) defines unambiguous written all-numeric big-endian formats for dates, such as 2022-12-31 for 31 December 2022, and time, such as 23:59:58 for 23 hours, 59 minutes, and 58 seconds. These standard notations have been adopted by many countries as a national standard, e ...