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AstroUtilsJulianDateUT1 Method
Current Julian date based on the UT1 time scale

Namespace: ASCOM.Astrometry.AstroUtils
Assembly: ASCOM.Astrometry (in ASCOM.Astrometry.dll) Version: (
public double JulianDateUT1(
	double DeltaUT1


Type: SystemDouble
Current value for Delta-UT1, the difference between UTC and UT1; always in the range -0.9 to +0.9 seconds. Use 0.0 if you do not know this value; it varies irregularly throughout the year.

Return Value

Type: Double
Double - Julian date on the UT1 timescale.
UT1 time is calculated as UT1 = UTC + DeltaUT1 when DeltaUT1 is non zero. otherwise it is calaulcated through TAI and DeltaT. This value is then converted to a Julian date and returned.

When Delta-UT1 is provided, UT1 is calculated as UT1 = UTC + DeltaUT1. Otherwise, when Delta-UT1 is 0.0, DeltaUT1 is calculated as DeltaUT1 = TT - DeltaT = UTC + ΔAT + 32.184s - DeltaT, where ΔAT is the current number of leap seconds applied to UTC (34 at April 2012, with the 35th being added at the end of June 2012).

Forecast values of DUT1 are published by IERS Bulletin A at

See Also