astro::coords Namespace Reference

Classes
struct	EquatorialCoord
	Represents a position in the equatorial coordinate system. More...
struct	EclipticCoord
	Represents a position in the ecliptic coordinate system. More...
struct	HorizontalCoord
	Represents a position in the horizontal coordinate system. More...
struct	Fk5Correction
	Ecliptic longitude and latitude corrections from VSOP87D to FK5. More...

Functions
auto	fk5_correction (const double jde_tt, const toolbox::SphericalCoordinate &vsop87d_coord) -> Fk5Correction
	Calculate the FK5 correction for dynamical ecliptic coordinates of date.
auto	ecliptic_to_equatorial (const toolbox::AngleDeg &λ, const toolbox::AngleDeg &β, const toolbox::AngleDeg &ε) -> EquatorialCoord
	Convert ecliptic coordinates (λ, β) to equatorial coordinates (α, δ).
auto	equatorial_to_horizontal (const toolbox::AngleDeg &H, const toolbox::AngleDeg &δ, const toolbox::AngleDeg &φ) -> HorizontalCoord
	Convert equatorial coordinates (H, δ) to horizontal coordinates (A, h) for an observer at latitude φ.

Function Documentation

ecliptic_to_equatorial()

auto astro::coords::ecliptic_to_equatorial ( const toolbox::AngleDeg & λ, const toolbox::AngleDeg & β, const toolbox::AngleDeg & ε )->EquatorialCoord

inlinenodiscard

Convert ecliptic coordinates (λ, β) to equatorial coordinates (α, δ).

Parameters

λ	The ecliptic longitude.
β	The ecliptic latitude.
ε	The obliquity of the ecliptic. Use the true obliquity (ε₀ + Δε) for apparent coordinates.

Returns

The equatorial coordinates (α, δ); α is normalized to [0°, 360°).

Note

Meeus gives tan α in terms of tan β, which diverges at the ecliptic poles (β = ±90°). Here the numerator and denominator are multiplied through by cos β, so the result stays finite.

Assumes β ∈ [-90°, 90°], as ecliptic latitude is by definition; outside that range cos β < 0 and the cos β-multiplied form silently shifts α by 180°.

See also

Jean Meeus, "Astronomical Algorithms", Second Edition, Chapter 13, Formulas (13.3) and (13.4).

equatorial_to_horizontal()

auto astro::coords::equatorial_to_horizontal ( const toolbox::AngleDeg & H, const toolbox::AngleDeg & δ, const toolbox::AngleDeg & φ )->HorizontalCoord

inlinenodiscard

Convert equatorial coordinates (H, δ) to horizontal coordinates (A, h) for an observer at latitude φ.

Parameters

H	The local hour angle of the object, measured westward from the meridian.
δ	The declination of the object.
φ	The observer's geographic latitude.

Returns

The horizontal coordinates (A, h); A is measured from the south point, positive westward, and normalized to [0°, 360°).

Note

Meeus gives tan A in terms of tan δ, which diverges at the celestial poles (δ = ±90°). Here the numerator and denominator are multiplied through by cos δ, so the result stays finite.

Assumes δ ∈ [-90°, 90°] and φ ∈ [-90°, 90°], as declination and geographic latitude are by definition; outside the former range the cos δ-multiplied form silently shifts A by 180°.

The resulting altitude is purely geometric: no atmospheric refraction, parallax, or horizon dip is taken into account (for refraction see Meeus Chapter 16; for parallax, Chapter 40).

See also

Jean Meeus, "Astronomical Algorithms", Second Edition, Chapter 13, Formulas (13.5) and (13.6).

fk5_correction()

auto astro::coords::fk5_correction ( const double jde_tt, const toolbox::SphericalCoordinate & vsop87d_coord )->Fk5Correction

inlinenodiscard

Calculate the FK5 correction for dynamical ecliptic coordinates of date.

Parameters

jde_tt	Julian Ephemeris Day in TT.
vsop87d_coord	Dynamical ecliptic coordinates at the same epoch; radius is unused.

Returns

Additive longitude and latitude corrections.

See also

Jean Meeus, "Astronomical Algorithms", Second Edition, Formula (32.3); Chapter 33, page 225 for geocentric coordinates.