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NOVAS31Era Method

Returns the value of the Earth Rotation Angle (theta) for a given UT1 Julian date.

Namespace:  ASCOM.Astrometry.NOVAS
Assembly:  ASCOM.Astrometry (in ASCOM.Astrometry.dll) Version: 3c9121baba46811fe6e53a58a05935662261416d
public double Era(
	double JdHigh,
	double JdLow


Type: SystemDouble
High-order part of UT1 Julian date.
Type: SystemDouble
Low-order part of UT1 Julian date.

Return Value

Type: Double
The Earth Rotation Angle (theta) in degrees.
The expression used is taken from the note to IAU Resolution B1.8 of 2000. 1. The algorithm used here is equivalent to the canonical theta = 0.7790572732640 + 1.00273781191135448 * t, where t is the time in days from J2000 (t = JdHigh + JdLow - T0), but it avoids many two-PI 'wraps' that decrease precision (adopted from SOFA Fortran routine iau_era00; see also expression at top of page 35 of IERS Conventions (1996)).
See Also