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In this formulation a measurement or calculation of EOT at a certain value of time depends on a measurement or calculation of α at that time. Both α and α M vary from 0 to 24 hours during the course of a year. The former has a discontinuity at a time that depends on the value of UT, while the latter has its at a slightly later time.
Local mean time (LMT) is a form of solar time that corrects the variations of local apparent time, forming a uniform time scale at a specific longitude. This measurement of time was used for everyday use during the 19th century before time zones were introduced beginning in the late 19th century; it still has some uses in astronomy and navigation.
A plot of hours of daylight as a function of the date for changing latitudes. This plot was created using the simple sunrise equation, approximating the sun as a single point and does not take into account effects caused by the atmosphere or the diameter of the Sun.
Time zones of the world. A time zone is an area which observes a uniform standard time for legal, commercial and social purposes. Time zones tend to follow the boundaries between countries and their subdivisions instead of strictly following longitude, because it is convenient for areas in frequent communication to keep the same time.
The concept was touted as an alternative, decimal measure of time. One of the supposed goals was to simplify the way people in different time zones communicate about time, mostly by eliminating time zones altogether. It also does away with the division of the day into 12 or 24 parts (hours), then 60 parts (minutes), then 60 parts (seconds ...
The tz database partitions the world into regions where local clocks all show the same time. This map was made by combining version 2023d with OpenStreetMap data, using open source software. [1] This is a list of time zones from release 2024b of the tz database. [2]
In modern usage, GMT is no longer a formal standard reference time: it is now a name for the time zone UTC+00:00. Universal Time is now determined by reference to distant celestial objects: UTC is derived from International Atomic Time (TAI), and is adjusted by leap seconds to compensate for variations in the rotational velocity of the Earth. [ 3 ]
Fractional days are often calculated in UTC or TT, although Julian Dates use pre-1925 astronomical date/time (each date began at noon = ".0") and Microsoft Excel uses the local time zone of the computer. Using fractional days reduces the number of units in time calculations from four (days, hours, minutes, seconds) to just one (days).