astro::earth::aberration Namespace Reference

Classes
struct	DailyVariationTerm
	A term of the Δλ series: amplitude × τ^tau_power × sin(phase + rate × τ), with τ the Julian millennia since J2000. More...

Functions
auto	daily_λ_variation (const double jde) -> double
	The daily variation Δλ of the Sun's geocentric longitude, mean equinox of the date.
auto	compute (const double jde, const toolbox::DistanceAu r) -> toolbox::AngleDeg
	Compute the aberration correction to the Sun's geometric longitude, Meeus (25.11).

Variables
constexpr std::array< DailyVariationTerm, 21 >	MEEUS_DAILY_VARIATION_TERMS
	The Δλ series (daily variation of the Sun's geocentric longitude), p. 168.
constexpr double	LIGHT_TIME_DAYS_PER_AU
	The light-time for unit distance, in days per AU (= 499.00478 s ≈ 8.3 min).

Function Documentation

compute()

auto astro::earth::aberration::compute ( const double jde, const toolbox::DistanceAu r )->toolbox::AngleDeg

inlinenodiscard

Compute the aberration correction to the Sun's geometric longitude, Meeus (25.11).

Parameters

jde	The julian ephemeris day number, which is based on TT.
r	The Sun's radius vector.

Returns

The aberration (in degrees); subtract it from the geometric longitude.

Note

Meeus (25.11) applies the correction −(light-time) × R × Δλ to the geometric longitude; this function returns the positive magnitude, which the caller subtracts (sun.hpp). The variable form accounts for the perturbations of the Earth's orbit (mainly lunar) that the fixed form (25.10) −20.4898″/R ignores: error < 0.001″ vs up to 0.01″ for (25.10). The (25.10) numerator is κ(1−e²), not the bare aberration constant κ = 20.49552″ (#66).

See also

Jean Meeus, "Astronomical Algorithms", Second Edition, (25.10)-(25.11), p. 167-168.

daily_λ_variation()

auto astro::earth::aberration::daily_λ_variation ( const double jde ) ->double

inlinenodiscard

The daily variation Δλ of the Sun's geocentric longitude, mean equinox of the date.

Parameters

jde	The julian ephemeris day number, which is based on TT.

Returns

Δλ in arcseconds per day.

Note

The constant term is 3548.330 for the mean equinox of the date; 3548.193 is for the fixed J2000 frame (p. 168 note).

See also

Jean Meeus, "Astronomical Algorithms", Second Edition, p. 168.

Variable Documentation

LIGHT_TIME_DAYS_PER_AU

double astro::earth::aberration::LIGHT_TIME_DAYS_PER_AU

inlineconstexpr

The light-time for unit distance, in days per AU (= 499.00478 s ≈ 8.3 min).

Note

This stored value is the fixed ten-decimal rounding of ERFA_DAU / ERFA_CMPS / ERFA_DAYSEC, not a digit copy of ERFA_AULT.

See also

ERFA v2.0.1 erfam.h.

MEEUS_DAILY_VARIATION_TERMS

std::array<DailyVariationTerm, 21> astro::earth::aberration::MEEUS_DAILY_VARIATION_TERMS

inlineconstexpr

The Δλ series (daily variation of the Sun's geocentric longitude), p. 168.

Note

Terms with rate 359993/719987/1079981 are due to the eccentricity, 4452671/9224659/4092677 to the Moon, 450368/225184/315559/675553 to Venus, 329644/659289/299295 to Jupiter, 337181 to Mars.