﻿SOFA.UtcTai Method

Time scale transformation: Coordinated Universal Time, UTC, to International Atomic Time, TAI.

Namespace:  ASCOM.Astrometry.SOFA
Assembly:  ASCOM.Astrometry (in ASCOM.Astrometry.dll) Version: 3c9121baba46811fe6e53a58a05935662261416d
Syntax
```public int UtcTai(
double utc1,
double utc2,
ref double tai1,
ref double tai2
)```

#### Parameters

utc1
Type: SystemDouble
UTC as a 2-part quasi Julian Date (Notes 1-4)
utc2
Type: SystemDouble
UTC as a 2-part quasi Julian Date (Notes 1-4)
tai1
Type: SystemDouble
TAI as a 2-part Julian Date (Note 5)
tai2
Type: SystemDouble
TAI as a 2-part Julian Date (Note 5)

#### Return Value

Type: Int32
Status: +1 = dubious year (Note 3) 0 = OK -1 = unacceptable date
Remarks
Notes:
1. utc1+utc2 is quasi Julian Date (see Note 2), apportioned in any convenient way between the two arguments, for example where utc1 is the Julian Day Number and utc2 is the fraction of a day.
2. JD cannot unambiguously represent UTC during a leap second unless special measures are taken. The convention in the present function is that the JD day represents UTC days whether the length is 86399, 86400 or 86401 SI seconds. In the 1960-1972 era there were smaller jumps (in either direction) each time the linear UTC(TAI) expression was changed, and these "mini-leaps" are also included in the SOFA convention.
3. The warning status "dubious year" flags UTCs that predate the introduction of the time scale or that are too far in the future to be trusted. See iauDat for further details.
4. The function iauDtf2d converts from calendar date and time of day into 2-part Julian Date, and in the case of UTC implements the leap-second-ambiguity convention described above.
5. The returned TAI1,TAI2 are such that their sum is the TAI Julian Date.