NovasEra Method

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

Definition

Namespace: ASCOM.Tools.Novas31
Assembly: ASCOM.AstrometryTools (in ASCOM.AstrometryTools.dll) Version: 3.0.0-rc.1+86c25ce733aebb4d8b1b8a62e84770ea5e972bea

C#

public static double Era(
	double JdHigh,
	double JdLow
)

VB

Public Shared Function Era ( 
	JdHigh As Double,
	JdLow As Double
) As Double

Parameters

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

Return Value

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)).

Version Information

.NET Standard

Supported in: 2.0