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 (6.1.1.2619)

Syntax

C#
public double Era(
	double JdHigh,
	double JdLow
)
Visual Basic
Public Function Era ( _
	JdHigh As Double, _
	JdLow As Double _
) As Double
Visual C++
public:
virtual double Era(
	double JdHigh, 
	double JdLow
) sealed

Parameters

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

Return Value

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