Overview Time scale Specification of the correct time is particularly important. Various time scales are in use. The Solar Position Algorithm is based on Universal Time (UT1). Universal Time (UT1) Between 1928 and 1968 was the UT was the accepted world time. It is also referred to as universal solar time. It is determined through astronomic observation of the angle of rotation of the earth and corresponds to the mean local time of the observatory at Greenwich (prime meridian). This parameter is derived from the earth's rotation and takes into account fluctuations and long-term slowdown and is therefore not strictly a uniform measure of time.
On the other hand, it is always synchronised with the actual change-over between day and night. International Atomic Time (TAI) The International Atomic Time is specified by more than 50 time institutes worldwide, based on their atomic clocks. An atomic time is based on an atomic standard time that can be assumed to be exactly uniform. Coordinated Universal Time (UTC) The coordinated world time UTC has been used as the standard world time since 1968. This is the time referred to by GMT in everyday usage. Greenwich Mean Time (GMT) was the original world time before 1928. UTC continues to use the observatory at Greenwich (prime meridian) as point of reference.
The earth's time zones are derived from the coordinated world time (UTC+1 = Central European Time). In contrast to UT1, its second cycle matches the exactly uniform second cycle of the International Atomic Time (TAI). Leap seconds are used to compensate the difference between UTC and UT1. The difference between the UT1 reference time is always less than one second. The coordinated world time UTC is therefore a compromise between UT1 and TAI. The following formula is used to convert a time from UTC to UT1: UT1 = UTC + DUT1 Terrestrial Time (TT) Also referred to as Terrestrial Dynamical Time (TDT).
This time is used as the basis for calculating astronomic events and is based on the exactly uniform seconds of the International Atomic Time (TAI). The following applies: TT = TAI + 32.184 Leap Seconds To synchronise the coordinated world time UTC with UT1, a leap second is added when required. This additional second is specified by the International Earth Rotation and Reference Systems Service (IERS) at irregular, non-predictable intervals. It ensures that the difference between the two time scales is always less than one second. (In the past such additional leap seconds have always been added on 31 December or 30 June after 23:59:59 UTC.) DUT1 denotes the remaining difference.
The following applies: DUT1 = UT1 - UTC This value is derived from observations that are continuously reported . Delta T TS3900 9 Version: 1.1 Place Longitude Latitude Sydney, Australia 151.2° -33.9° New York, USA -74.0° 40.7° London, England -0.1° 51.5° Moscow, Russia 37.6° 55.7° Peking, China 116.3° 39.9° Dubai, United Arab Emirates 55.3° 25.4° Rio de Janeiro, Brazil -43.2° -22.9° Hawaii, USA -155.8° 20.2° Verl, Germany 8.5° 51.9°