Home - News ( United States | United Kingdom | Italy | Germany ) - Football scores

Showing content from https://smithsonian.github.io/SuperNOVAS/apidoc/html/equinox_8c.html below:

SuperNOVAS: src/equinox.c File Reference

Date

Created on Mar 6, 2025

Various function for calculating the equator and equinox of date, and related quatities.

Returns the general precession in longitude (Simon et al. 1994), equivalent to 5028.8200 arcsec/cy at J2000.

Parameters

t [cy] Julian centuries since J2000

Returns

[rad] the approximate precession angle [-π:π].

See also

planet_lon()

nutation_angles()

ee_ct()

NOVAS_JD_J2000

Since

1.0

Author

Attila Kovacs

References TWOPI.

Specifies the unmodeled celestial pole offsets for high-precision applications to be applied to the True of Date (TOD) equator, in the old, pre IAU 2006 methodology. These offsets must not include tidal terms, and should be specified relative to the IAU2006 precession/nutation model to provide a correction to the modeled (precessed and nutated) position of Earth's pole, such those derived from observations and published by IERS.

The call sets the global variables PSI_COR and EPS_COR, for subsequent calls to e_tilt(). As such, it should be called to specify pole offsets prior to legacy NOVAS C equinox-specific calls. The global values of PSI_COR and EPS_COR specified via this function will be effective until explicitly changed again.

NOTES:

1. The pole offsets et this way will affect all future TOD-based calculations, until the pole is changed or reset again. Hence, you should be extremely careful using it (if at all), as it may become an unpredictable source of inaccuracy if implicitly applied without intent to do so.
2. The current UT1 - UTC time difference, and polar offsets, historical data and near-term projections are published in the <a href="https://www.iers.org/IERS/EN/Publications/Bulletins/bulletins.html>IERS Bulletins
3. If Δδψ, Δδdε offsets are specified, these must be the residual corrections relative to the IAU 2006 precession/nutation model (not the Lieske et al. 1977 model!). As such, they are just a rotated version of the newer dx, dy offsets published by IERS.
4. The equivalent IAU 2006 standard is to apply dx, dy pole offsets only for converting between TIRS and ITRS, e.g. via wobble()).
5. There is no need to define pole offsets this way when using the newer frame-based approach introduced in SuperNOVAS. If the pole offsets are specified on a per-frame basis during the initialization of each observing frame, the offsets will be applied for the TIRS / ITRS conversion only, and not to the TOD equator per se.

REFERENCES:

1. Kaplan, G. (2005), US Naval Observatory Circular 179.
2. Kaplan, G. (2003), USNO/AA Technical Note 2003-03.

Parameters

jd_tt [day] Terrestrial Time (TT) based Julian date. Used only if 'type' is POLE_OFFSETS_X_Y (2), to transform dx and dy to the equivalent Δδψ and Δδε values. type POLE_OFFSETS_DPSI_DEPS (1) if the offsets are Δδψ, Δδε relative to the IAU 20006 precession/nutation model; or POLE_OFFSETS_X_Y (2) if they are dx, dy offsets relative to the IAU 2000/2006 precession-nutation model. dpole1 [mas] Value of celestial pole offset in first coordinate, (Δδψ for or dx) in milliarcseconds, relative to the IAU2006 precession/nutation model. dpole2 [mas] Value of celestial pole offset in second coordinate, (Δδε or dy) in milliarcseconds, relative to the IAU2006 precession/nutation model.

Returns

0 if successful, or else 1 if 'type' is invalid.

See also

wobble()

e_tilt()

place()

cirs_to_itrs()

tod_to_itrs()

get_ut1_to_tt()

sidereal_time()

NOVAS_FULL_ACCURACY

Deprecated:

This old way of incorporating Earth orientation parameters into the true equator and equinox is now disfavored. Instead, wobble() should be used to convert between the Terrestrial Intermediate Reference System (TIRS) / Pseudo Earth Fixed (PEF) and the International Terrestrial Reference System (ITRS) going forward.

References POLE_OFFSETS_DPSI_DEPS, and POLE_OFFSETS_X_Y.

Computes quantities related to the orientation of the Earth's rotation axis at the specified Julian date.

Unmodelled corrections to earth orientation can be defined via cel_pole() prior to this call.

NOTES:

1. This function caches the results of the last calculation in case it may be re-used at no extra computational cost for the next call.

Parameters

jd_tdb [day] Barycentric Dynamical Time (TDB) based Julian date. accuracy NOVAS_FULL_ACCURACY (0) or NOVAS_REDUCED_ACCURACY (1) [out] mobl [deg] Mean obliquity of the ecliptic. It may be NULL if not required. [out] tobl [deg] True obliquity of the ecliptic. It may be NULL if not required. [out] ee [s] Equation of the equinoxes in seconds of time. It may be NULL if not required. [out] dpsi [arcsec] Nutation in longitude. It may be NULL if not required. [out] deps [arcsec] Nutation in obliquity. It may be NULL if not required.

Returns

0 if successful, or -1 if the accuracy argument is invalid

See also

cel_pole()

place()

equ2ecl()

ecl2equ()

References ee_ct(), mean_obliq(), NOVAS_FULL_ACCURACY, NOVAS_REDUCED_ACCURACY, and nutation_angles().

Computes the "complementary terms" of the equation of the equinoxes. The input Julian date can be split into high and low order parts for improved accuracy. Typically, the split is into integer and fractiona parts. If the precision of a single part is sufficient, you may set the low order part to 0.

The series used in this function was derived from the first reference. This same series was also adopted for use in the IAU's Standards of Fundamental Astronomy (SOFA) software (i.e., subroutine eect00.for and function eect00.c).

The low-accuracy series used in this function is a simple implementation derived from the first reference, in which terms smaller than 2 microarcseconds have been omitted.

NOTES:

1. This function caches the results of the last calculation in case it may be re-used at no extra computational cost for the next call.

REFERENCES:

1. Capitaine, N., Wallace, P.T., and McCarthy, D.D. (2003). Astron. & Astrophys. 406, p. 1135-1149. Table 3.
2. IERS Conventions (2010), Chapter 5, p. 60, Table 5.2e.
   (Table 5.2e presented in the printed publication is a truncated series. The full series, which is used in NOVAS, is available on the IERS Conventions Center website: ftp://tai.bipm.org/iers/conv2010/chapter5/tab5.2e.txt)

Parameters

jd_tt_high [day] High-order part of TT based Julian date. jd_tt_low [day] Low-order part of TT based Julian date. accuracy NOVAS_FULL_ACCURACY (0) or NOVAS_REDUCED_ACCURACY (1)

Returns

[rad] Complementary terms, in radians.

See also

e_tilt()

cel_pole()

nutation()

sidereal_time()

Deprecated:

(for intrernal use) There is no good reason why this function should be exposed to users of the library. It is intended only for use by e_tilt() internally.

References accum_prec(), novas_delaunay_args::D, novas_delaunay_args::F, fund_args(), NOVAS_FULL_ACCURACY, NOVAS_MERCURY, NOVAS_NEPTUNE, NOVAS_REDUCED_ACCURACY, novas_delaunay_args::Omega, and planet_lon().

Compute the fundamental arguments (mean elements) of the Sun and Moon.

REFERENCES:

1. Simon et al. (1994) Astronomy and Astrophysics 282, 663-683, esp. Sections 3.4-3.5.

Parameters

t [cy] TDB time in Julian centuries since J2000.0 [out] a [rad] Fundamental arguments data to populate (5 doubles) [0:2π]

Returns

0 if successful, or -1 if the output pointer argument is NULL.

See also

nutation_angles()

ee_ct()

NOVAS_JD_J2000

References novas_norm_ang().

Compute the intermediate right ascension of the equinox at the input Julian date, using an analytical expression for the accumulated precession in right ascension. For the true equinox, the result is the equation of the origins.

NOTES:

1. Fixes bug in NOVAS C 3.1, which returned the value for the wrong 'equinox' if 'equinox = 1' was requested for the same 'jd_tbd' and 'accuracy' as a the preceding call with 'equinox = 0'. As a result, the caller ended up with the mean instead of the expected true equinox R.A. value.

REFERENCES:

1. Capitaine, N. et al. (2003), Astronomy and Astrophysics 412, 567-586, eq. (42).

Parameters

jd_tdb [day] Barycentric Dynamic Time (TDB) based Julian date equinox NOVAS_MEAN_EQUINOX (0) or NOVAS_TRUE_EQUINOX (1, or non-zero) accuracy NOVAS_FULL_ACCURACY (0) or NOVAS_REDUCED_ACCURACY (1, or non-zero)

Returns

[h] Intermediate right ascension of the equinox, in hours (+ or -). If 'equinox' = 1 (i.e true equinox), then the returned value is the equation of the origins.

See also

cio_location()

gcrs_to_cirs()

Deprecated:

(for internal use) There is no good reason why this function should be exposed to users. It is intended only for cio_location() internally.

References e_tilt(), NOVAS_FULL_ACCURACY, NOVAS_REDUCED_ACCURACY, and NOVAS_TRUE_EQUINOX.

Computes the mean obliquity of the ecliptic.

REFERENCES:

1. Capitaine et al. (2003), Astronomy and Astrophysics 412, 567-586.

Parameters

jd_tdb [day] Barycentric Dynamic Time (TDB) based Julian date

Returns

[arcsec] Mean obliquity of the ecliptic in arcseconds.

See also

e_tilt()

equ2ecl()

ecl2equ()

tt2tdb()

Nutates equatorial rectangular coordinates from mean equator and equinox of epoch to true equator and equinox of epoch. Inverse transformation may be applied by setting flag 'direction'.

This is the old (pre IAU 2006) method of nutation calculation. If you follow the now standard IAU 2000/2006 methodology you will want to use nutation_angles() instead.

REFERENCES:

1. Explanatory Supplement To The Astronomical Almanac, pp. 114-115.

Parameters

jd_tdb [day] Barycentric Dynamic Time (TDB) based Julian date direction NUTATE_MEAN_TO_TRUE (0) or NUTATE_TRUE_TO_MEAN (-1; or non-zero) accuracy NOVAS_FULL_ACCURACY (0) or NOVAS_REDUCED_ACCURACY (1) in Position 3-vector, geocentric equatorial rectangular coordinates, referred to mean equator and equinox of epoch. [out] out Position vector, geocentric equatorial rectangular coordinates, referred to true equator and equinox of epoch. It can be the same as the input position.

Returns

0 if successful, or -1 if one of the vector arguments is NULL.

See also

nutation_angles()

tt2tdb()

NOVAS_TOD

References e_tilt(), and NUTATE_MEAN_TO_TRUE.

Returns the planetary longitude, for Mercury through Neptune, w.r.t. mean dynamical ecliptic and equinox of J2000, with high order terms omitted (Simon et al. 1994, 5.8.1-5.8.8).

Parameters

t [cy] Julian centuries since J2000 planet Novas planet id, e.g. NOVAS_MARS.

Returns

[rad] The approximate longitude of the planet in radians [-π:π], or NAN if the planet id is out of range.

See also

accum_prec()

nutation_angles()

ee_ct()

NOVAS_JD_J2000

Since

1.0

Author

Attila Kovacs

References NOVAS_NEPTUNE, and TWOPI.

Precesses equatorial rectangular coordinates from one epoch to another. Unlike the original NOVAS routine, this routine works for any pairing of the time arguments.

This function calculates precession for the old (pre IAU 2000) methodology. Its main use for NOVAS users is to allow converting older catalog coordinates e.g. to J2000 coordinates, which then can be converted to the now standard ICRS system via frame_tie().

NOTE:

1. Unlike the original NOVAS C 3.1 version, this one does not require that one of the time arguments must be J2000. You can precess from any date to any other date, and the intermediate epoch of J2000 will be handled internally as needed.

2. This function caches the results of the last calculation in case it may be re-used at no extra computational cost for the next call.

REFERENCES:

1. Explanatory Supplement To The Astronomical Almanac, pp. 103-104.
2. Capitaine, N. et al. (2003), Astronomy And Astrophysics 412, pp. 567-586.
3. Hilton, J. L. et al. (2006), IAU WG report, Celest. Mech., 94, pp. 351-367.
4. Capitaine, N., P.T. Wallace and J. Chapront (2005), “Improvement of the IAU 2000 precession model.” Astronomy & Astrophysics, Vol. 432, pp. 355–67.
5. Liu, J.-C., &amp Capitaine, N. (2017), A&A 597, A83

Parameters

jd_tdb_in [day] Barycentric Dynamic Time (TDB) based Julian date of the input epoch in Position 3-vector, geocentric equatorial rectangular coordinates, referred to mean dynamical equator and equinox of the initial epoch. jd_tdb_out [day] Barycentric Dynamic Time (TDB) based Julian date of the output epoch [out] out Position 3-vector, geocentric equatorial rectangular coordinates, referred to mean dynamical equator and equinox of the final epoch. It can be the same vector as the input.

Returns

0 if successful, or -1 if either of the position vectors is NULL.

See also

nutation()

frame_tie()

novas_epoch()

tt2tdb()

cio_basis()

NOVAS_TOD

NOVAS_JD_J2000

NOVAS_JD_B1950

NOVAS_JD_B1900

References precession().

RetroSearch is an open source project built by @garambo | Open a GitHub Issue

Search and Browse the WWW like it's 1997 | Search results from DuckDuckGo

HTML: 3.2 | Encoding: UTF-8 | Version: 0.7.4