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Earth's rate of rotation must be integrated to obtain time, which is Earth's angular position (specifically, the orientation of the meridian of Greenwich relative to the fictitious mean sun). Integrating +1.7 ms/d/cy and centering the resulting parabola on the year 1820 yields (to a first approximation) 32 × ( year − 1820 / 100 ) 2
In a time period from 1959 to 1998, NIST developed a series of seven caesium-133 microwave clocks named NBS-1 to NBS-6 and NIST-7 after the agency changed its name from the National Bureau of Standards to the National Institute of Standards and Technology. [10] The first clock had an accuracy of 10 −11, and the last clock had an accuracy of ...
International Atomic Time (abbreviated TAI, from its French name temps atomique international [1]) is a high-precision atomic coordinate time standard based on the notional passage of proper time on Earth's geoid. [2] TAI is a weighted average of the time kept by over 450 atomic clocks in over 80 national laboratories worldwide. [3]
Low back pain is not a specific disease but rather a complaint that may be caused by a large number of underlying problems of varying levels of seriousness. [30] The majority of low back pain does not have a clear cause [1] but is believed to be the result of non-serious muscle or skeletal issues such as sprains or strains. [31]
Chronic back strain occurs because of the sustained trauma and wearing out of the back muscles. [1] Acute back strain can occur following a single instance of over stressing of back muscles, as in lifting a heavy object. Chronic back strain is more common than the acute type. To avoid back strain it is important to bend the knees whenever you ...
Terrestrial Time (TT) is a modern astronomical time standard defined by the International Astronomical Union, primarily for time-measurements of astronomical observations made from the surface of Earth. [1] For example, the Astronomical Almanac uses TT for its tables of positions (ephemerides) of the Sun, Moon and planets as seen from Earth.
For example, considered over the total time-span of Earth (4.6 billion years), a clock set in a geostationary position at an altitude of 9,000 meters above sea level, such as perhaps at the top of Mount Everest (prominence 8,848 m), would be about 39 hours ahead of a clock set at sea level.