Classes
struct	EquatorialAngles
	The equatorial precession angles of Meeus (21.2): ζ (zeta), z, θ (theta), in degrees. More...
struct	EclipticAngles
	The ecliptic precession quantities of Meeus (21.5): η (eta), Π (Pi), p, in degrees. More...

Functions
auto	equatorial_angles (const double jde_from, const double jde_to) -> EquatorialAngles
	Compute the equatorial precession angles ζ, z, θ between two epochs.
auto	equatorial (const toolbox::AngleDeg &α0, const toolbox::AngleDeg &δ0, const double jde_from, const double jde_to) -> astro::coords::EquatorialCoord
	Apply equatorial precession, carrying (α₀, δ₀) from one epoch to another.
auto	ecliptic_angles (const double jde_from, const double jde_to) -> EclipticAngles
	Compute the ecliptic precession quantities η, Π, p between two epochs.
auto	ecliptic (const toolbox::AngleDeg &λ0, const toolbox::AngleDeg &β0, const double jde_from, const double jde_to) -> astro::coords::EclipticCoord
	Apply ecliptic precession, carrying (λ₀, β₀) from one epoch to another.

Function Documentation

◆ ecliptic()

auto astro::earth::precession::ecliptic	(	const toolbox::AngleDeg &	λ0,
		const toolbox::AngleDeg &	β0,
		const double	jde_from,
		const double	jde_to )->astro::coords::EclipticCoord

inlinenodiscard

Apply ecliptic precession, carrying (λ₀, β₀) from one epoch to another.

Parameters

λ0	Ecliptic longitude at the initial epoch.
β0	Ecliptic latitude at the initial epoch.
jde_from	The Julian ephemeris day of the initial epoch.
jde_to	The Julian ephemeris day of the final epoch.

Returns: The precessed coordinates (λ, β); λ is normalized to [0°, 360°), β lies in [-90°, 90°].

Note: This is precession only — proper motion, nutation, and aberration are not applied.; sin β = C (Meeus 21.7); C is clamped to [-1, 1] for the same pole-roundoff reason as δ in equatorial() above.

See also: Jean Meeus, "Astronomical Algorithms", Second Edition, Chapter 21, Formula (21.7).

auto astro::earth::precession::ecliptic_angles	(	const double	jde_from,
		const double	jde_to )->EclipticAngles

inlinenodiscard

Compute the ecliptic precession quantities η, Π, p between two epochs.

Parameters

jde_from	The Julian ephemeris day of the initial epoch (pass J2000 for catalogue-to-date).
jde_to	The Julian ephemeris day of the final epoch.

Returns: {η, Π, p} in degrees; Π carries the constant 174.876384°, p's linear term is the ~50.29"/year general precession in longitude. @see Jean Meeus, "Astronomical Algorithms", Second Edition, Chapter 21, Formula (21.5).

auto astro::earth::precession::equatorial	(	const toolbox::AngleDeg &	α0,
		const toolbox::AngleDeg &	δ0,
		const double	jde_from,
		const double	jde_to )->astro::coords::EquatorialCoord

inlinenodiscard

Apply equatorial precession, carrying (α₀, δ₀) from one epoch to another.

Parameters

α0	Right ascension at the initial epoch.
δ0	Declination at the initial epoch.
jde_from	The Julian ephemeris day of the initial epoch.
jde_to	The Julian ephemeris day of the final epoch.

Returns: The precessed coordinates (α, δ); α is normalized to [0°, 360°), δ lies in [-90°, 90°].

Note: This is precession only — proper motion, nutation, and aberration are not applied.; sin δ = C (Meeus 21.4); C is clamped to [-1, 1] against the roundoff that, when the precessed position falls near the pole, pushes it just past ±1 and would make asin return NaN.

See also: Jean Meeus, "Astronomical Algorithms", Second Edition, Chapter 21, Formula (21.4).

auto astro::earth::precession::equatorial_angles	(	const double	jde_from,
		const double	jde_to )->EquatorialAngles

inlinenodiscard

Compute the equatorial precession angles ζ, z, θ between two epochs.

Parameters

jde_from	The Julian ephemeris day of the initial epoch (pass J2000 for catalogue-to-date).
jde_to	The Julian ephemeris day of the final epoch.

Returns: {ζ, z, θ} in degrees; ζ and z nearly coincide for a small Δt, θ is the tilting angle.

See also: Jean Meeus, "Astronomical Algorithms", Second Edition, Chapter 21, Formula (21.2).; ERFA v2.0.1 prec76.c.