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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: 6.0.0.0 (6.2.0.2774)
Syntax
public double Era(
	double JdHigh,
	double JdLow
)

Parameters

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

Return Value

Type: Double
The Earth Rotation Angle (theta) in degrees.
Remarks
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