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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.
The United States Naval Observatory states "the Equation of Time is the difference apparent solar time minus mean solar time", i.e. if the sun is ahead of the clock the sign is positive, and if the clock is ahead of the sun the sign is negative. [6] [7] The equation of time is shown in the upper graph above for a period of slightly more than a ...
Using the Equation of time correction along with the time averaged ascending/descending noon sights can result in accuracies of 1 nautical mile (1.9 km) or less. Without time averaging, the difficulties in determining the exact moment of local noon due to the flattening of the Sun’s arc across the sky reduce the accuracy of calculation.
On a prograde planet like the Earth, the sidereal day is shorter than the solar day. At time 1, the Sun and a certain distant star are both overhead. At time 2, the planet has rotated 360° and the distant star is overhead again (1→2 = one sidereal day). But it is not until a little later, at time 3, that the Sun is overhead again (1→3 = one solar day). More simply, 1→2 is a complete ...
J transit is the Julian date for the local true solar transit (or solar noon). 2451545.0 is noon of the equivalent Julian year reference. 0.0053 sin M − 0.0069 sin ( 2 λ ) {\displaystyle 0.0053\sin M-0.0069\sin \left(2\lambda \right)} is a simplified version of the equation of time .
Longitude calculations can be simplified using a clock is set to the local time of a starting point whose longitude is known, transporting it to a new location, and using it for astronomical observations. The longitude of the new location can be determined by comparing the difference of local mean time and the time of the transported clock.
Local time is the time observed in a specific locality. There is no canonical definition. Originally it was mean solar time, but since the introduction of time zones it is generally the time as determined by the time zone in effect, with daylight saving time where and when applicable. [1] In some places this is known as standard time.
In former times, before the distribution of accurate time signals, it was part of the routine work at any observatory to observe the sidereal times of meridian transit of selected 'clock stars' (of well-known position and movement), and to use these to correct observatory clocks running local mean sidereal time; but nowadays local sidereal time ...