sofars 0.6.0

Pure Rust implementation of the IAU SOFA library
Documentation 
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90

use crate::consts::{DJ00, DJC};
use crate::pnp::nut00a;

///
///  IAU 2000A nutation with adjustments to match the IAU 2006
///  precession.
///
///  Given:
///     date1,date2   double   TT as a 2-part Julian Date (Note 1)
///
///  Returned:
///     dpsi,deps     double   nutation, luni-solar + planetary (Note 2)
///
///  Status:  canonical model.
///
///  Notes:
///
///  1) The TT date date1+date2 is a Julian Date, apportioned in any
///     convenient way between the two arguments.  For example,
///     JD(TT)=2450123.7 could be expressed in any of these ways,
///     among others:
///
///            date1          date2
///
///         2450123.7           0.0       (JD method)
///         2451545.0       -1421.3       (J2000 method)
///         2400000.5       50123.2       (MJD method)
///         2450123.5           0.2       (date & time method)
///
///     The JD method is the most natural and convenient to use in
///     cases where the loss of several decimal digits of resolution
///     is acceptable.  The J2000 method is best matched to the way
///     the argument is handled internally and will deliver the
///     optimum resolution.  The MJD method and the date & time methods
///     are both good compromises between resolution and convenience.
///
///  2) The nutation components in longitude and obliquity are in radians
///     and with respect to the mean equinox and ecliptic of date,
///     IAU 2006 precession model (Hilton et al. 2006, Capitaine et al.
///     2005).
///
///  3) The function first computes the IAU 2000A nutation, then applies
///     adjustments for (i) the consequences of the change in obliquity
///     from the IAU 1980 ecliptic to the IAU 2006 ecliptic and (ii) the
///     secular variation in the Earth's dynamical form factor J2.
///
///  4) The present function provides classical nutation, complementing
///     the IAU 2000 frame bias and IAU 2006 precession.  It delivers a
///     pole which is at current epochs accurate to a few tens of
///     microarcseconds, apart from the free core nutation.
///
///  Called:
///     iauNut00a    nutation, IAU 2000A
///
///  References:
///
///     Chapront, J., Chapront-Touze, M. & Francou, G. 2002,
///     Astron.Astrophys. 387, 700
///
///     Lieske, J.H., Lederle, T., Fricke, W. & Morando, B. 1977,
///     Astron.Astrophys. 58, 1-16
///
///     Mathews, P.M., Herring, T.A., Buffet, B.A. 2002, J.Geophys.Res.
///     107, B4.  The MHB_2000 code itself was obtained on 9th September
///     2002 from ftp//maia.usno.navy.mil/conv2000/chapter5/IAU2000A.
///
///     Simon, J.-L., Bretagnon, P., Chapront, J., Chapront-Touze, M.,
///     Francou, G., Laskar, J. 1994, Astron.Astrophys. 282, 663-683
///
///     Souchay, J., Loysel, B., Kinoshita, H., Folgueira, M. 1999,
///     Astron.Astrophys.Supp.Ser. 135, 111
///
///     Wallace, P.T., "Software for Implementing the IAU 2000
///     Resolutions", in IERS Workshop 5.1 (2002)
pub fn nut06a(date1: f64, date2: f64) -> (f64, f64) {
    /* Interval between fundamental date J2000.0 and given date (JC). */
    let t = ((date1 - DJ00) + date2) / DJC;

    /* Factor correcting for secular variation of J2. */
    let fj2 = -2.7774e-6 * t;

    /* Obtain IAU 2000A nutation. */
    let (dp, de) = nut00a(date1, date2);

    /* Apply P03 adjustments (Wallace & Capitaine, 2006, Eqs.5). */
    let dpsi = dp + dp * (0.4697e-6 + fj2);
    let deps = de + de * fj2;

    (dpsi, deps)
}