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Any predetermined amount of time that is accepted as a standard for measuring or expressing duration is referred to as a "unit of time." The second, which is defined as roughly 9 billion oscillations of the caesium atom, is the fundamental time unit of the International System of Units (SI) and, by extension, most of the Western world. In the modern SI system, "[the second] is defined by taking the fixed numerical value of the cesium frequency," ΔνCs , the frequency of the cesium 133 atom in its unperturbed ground-state hyperfine transition, to be 9 192 631 770 in the unit Hz, which is equal to s1. "
Time was often measured in terms of astronomical events in the past.
- Solar-based; during this year, Earth completed one revolution around the sun The Olympiad (4 years), the lustrum (5 years), the indiction (15 years), the decade (10 years), the century (100 years), and the millennium (1000 years).
- Using the Moon's orbital period around the Earth as the basis for the month
- Earth-based [a href="MY_REDIRECT_PREFIXhttps://en.wikipedia.org/wiki/Wikipedia:Citation_needed" target="_blank">span>citation needed/span>]; the time it takes for the Earth to rotate on its own axis, as measured by a sundial. The seven-day week and the fourteen-day fortnight both have their origins in this base. The hour (1/24 of a day) is one of the day's divisions; the minute (60 seconds) and the second (3600 seconds) came next. The second one was adopted as the scientific international unit (SI units).
- Using the apparent motion of the stars and constellations across the sky, sidereal time is used to determine the passage of time on the celestial sphere.
It is necessary to intercalate these units because their relationships are inconsistent. Because 12 times 28 is 336, which is less than 365, a year cannot be divided into 12 months of 28 days each. According to the moon's orbital definition, a lunar month has exactly 28 3 days According to the Gregorian calendar, this is the year 365.2425 months require correction for leap years and leap seconds As a result, scientific definitions of these units are now based on multiples of seconds.
Time can be measured in nanoseconds and milliseconds, both of which are multiples of a second.
Historical [ edit ]
Most ancient civilizations based their calendars on the solar year, the moon, and the 24-hour day. Sumerian, Egyptian, Chinese, Babylonian, ancient Attic, Buddhist, Hindu, Islamic, Icelandic, Mayan, and Republican-era French calendars are all examples of such systems.
The modern Gregorian calendar is based on the Julian calendar, which in turn was derived from the Roman calendar.
Scientific [ edit ]
- Light in a vacuum travels at the speed of the Jiffy, which is equal to one fermi (about the size of a nucleon) per second.
- Time taken by light to travel one Planck length is denoted by the Planck time.
- For engineering purposes, the TU (Time Unit) is defined as 1024 s.
- Sedimentation rates (typically of proteins) are measured in Svedbergs. It is defined as 100 fs, or 1013 seconds.
- The rotation of the galaxy provides the basis for the galactic year, which is typically expressed in millennia. 
- Using the geological time scale, we can correlate stratigraphy with epochs. Events in Earth's distant past are quantified and assigned to discrete time periods. The Cretaceous-Paleogene extinction event, for instance, marks the transition between the Cretaceous and Paleogene epochs. A supereon, which is made up of eons, is the largest unit of time. From eons, we get eras, which are further subdivided into decades, centuries, and epochs. It's not a real mathematical unit because different geological and historical events determine the length of different epochs, ages, periods, eras, and eons.
The light-year is not a measure of time, but rather a measure of distance (approximately 9 5.05 petameters (9.454254954880 km)
List [ edit ]Timing units
Interrelation [ edit ]
Formal time units are all multiples of each other in scale. The second, which is based on an atomic process, the day, which is an integral multiple of seconds, and the year, which is usually 365 days, are the most widely used units of time. These three units form the basis for all others.
See also [ edit ]
References [ edit ]
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