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This variation must be added to or subtracted from the UTC of local apparent noon to improve the accuracy of the calculation. 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 ...
Right: a few minutes later the Sun is on the local meridian again. A solar day is complete. Solar time is measured by the apparent diurnal motion of the Sun. Local noon in apparent solar time is the moment when the Sun is exactly due south or north (depending on the observer's latitude and the season). A mean solar day (what we normally measure ...
The apparent sun is the true sun as seen by an observer on Earth. [4] Apparent solar time or true solar time [a] is based on the apparent motion of the actual Sun. It is based on the apparent solar day, the interval between two successive returns of the Sun to the local meridian. [5] [6] Apparent solar time can be crudely measured by a sundial. [b]
Animation showing equation of time and analemma path over one year.. 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.
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 .
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.
Similar equations are coded into a Fortran 90 routine in Ref. [3] and are used to calculate the solar zenith angle and solar azimuth angle as observed from the surface of the Earth. Start by calculating n, the number of days (positive or negative, including fractional days) since Greenwich noon, Terrestrial Time, on 1 January 2000 .
The cosine of the hour angle (cos(h)) is used to calculate the solar zenith angle. At solar noon, h = 0.000 so cos(h) = 1, and before and after solar noon the cos(± h) term = the same value for morning (negative hour angle) or afternoon (positive hour angle), so that the Sun is at the same altitude in the sky at 11:00AM and 1:00PM solar time. [5]