sofars/erst/ee06a.rs
1use super::{gmst06, gst06a};
2use crate::vm::anpm;
3
4/// Equation of the equinoxes, IAU 2006/2000A
5///
6/// Equation of the equinoxes, compatible with IAU 2000 resolutions and
7/// IAU 2006/2000A precession-nutation.
8///
9/// This function is part of the International Astronomical Union's
10/// SOFA (Standards of Fundamental Astronomy) software collection.
11///
12/// Status: support function.
13///
14/// Given:
15/// ```
16/// date1,date2 double TT as a 2-part Julian Date (Note 1)
17/// ```
18/// Returned (function value):
19/// ```
20/// double equation of the equinoxes (Note 2)
21/// ```
22/// Notes:
23///
24/// 1) The TT date date1+date2 is a Julian Date, apportioned in any
25/// convenient way between the two arguments. For example,
26/// JD(TT)=2450123.7 could be expressed in any of these ways,
27/// among others:
28/// ```
29/// date1 date2
30///
31/// 2450123.7 0.0 (JD method)
32/// 2451545.0 -1421.3 (J2000 method)
33/// 2400000.5 50123.2 (MJD method)
34/// 2450123.5 0.2 (date & time method)
35/// ```
36/// The JD method is the most natural and convenient to use in
37/// cases where the loss of several decimal digits of resolution
38/// is acceptable. The J2000 method is best matched to the way
39/// the argument is handled internally and will deliver the
40/// optimum resolution. The MJD method and the date & time methods
41/// are both good compromises between resolution and convenience.
42///
43/// 2) The result, which is in radians, operates in the following sense:
44///
45/// Greenwich apparent ST = GMST + equation of the equinoxes
46///
47/// Called:
48/// ```
49/// iauAnpm normalize angle into range +/- pi
50/// iauGst06a Greenwich apparent sidereal time, IAU 2006/2000A
51/// iauGmst06 Greenwich mean sidereal time, IAU 2006
52/// ```
53/// Reference:
54///
55/// McCarthy, D. D., Petit, G. (eds.), 2004, IERS Conventions (2003),
56/// IERS Technical Note No. 32, BKG
57pub fn ee06a(date1: f64, date2: f64) -> f64 {
58 let _gst06a = gst06a(0.0, 0.0, date1, date2);
59 let _gmst06 = gmst06(0.0, 0.0, date1, date2);
60
61 // Equation of the equinoxes.
62 let ee = anpm(_gst06a - _gmst06);
63
64 ee
65}