Module nutation 

Nutation models for computing oscillations in Earth’s rotational axis.

Nutation is the short-period oscillation of Earth’s rotational axis about its mean position, superimposed on the longer-term precession. It arises from gravitational torques exerted by the Moon, Sun, and planets on Earth’s equatorial bulge. The principal component has a period of 18.6 years (the lunar nodal period) with an amplitude of about 9 arcseconds in obliquity.

This module provides implementations of the IAU standard nutation models:

Model	Lunisolar Terms	Planetary Terms	Precision	Use Case
NutationIAU2000A	678	687	~0.1 µas	High-precision astrometry, VLBI
NutationIAU2000B	77	0 (bias only)	~1 mas	General ephemeris, telescope pointing
NutationIAU2006A	678	687	~0.1 µas	Use with IAU 2006 precession

Output

All models return NutationResult containing:

• delta_psi: Nutation in longitude (radians)
• delta_eps: Nutation in obliquity (radians)

Time Argument

All compute(jd1, jd2) methods accept a two-part Julian Date in TDB (Barycentric Dynamical Time). The split preserves precision: typically jd1 = 2451545.0 (J2000.0) and jd2 = days from that epoch.

Example

use celestial_core::nutation::NutationIAU2006A;

let nutation = NutationIAU2006A::new();
let result = nutation.compute(2451545.0, 0.0).unwrap();

// At J2000.0: Δψ ≈ -0.04 arcsec, Δε ≈ -0.007 arcsec
println!("Δψ = {:.6} rad", result.delta_psi);
println!("Δε = {:.6} rad", result.delta_eps);

Sub-modules

• iau2000a: Full IAU 2000A model (678 lunisolar + 687 planetary terms)
• iau2000b: Truncated IAU 2000B model (77 terms + planetary bias)
• iau2006a: IAU 2000A with J2 corrections for IAU 2006 precession compatibility
• [fundamental_args]: Delaunay arguments and planetary mean longitudes
• lunisolar_terms: Coefficient table for lunisolar nutation series
• planetary_terms: Coefficient table for planetary nutation series
• types: NutationResult and NutationModel wrapper

Re-exports

pub use iau2000a::NutationIAU2000A;

pub use iau2000b::NutationIAU2000B;

pub use iau2006a::NutationIAU2006A;

pub use types::NutationModel;

pub use types::NutationResult;

Modules

iau2000a

IAU 2000A nutation model.

iau2000b

IAU 2000B Nutation Model

iau2006a

IAU 2006A nutation model.

lunisolar_terms

planetary_terms

types

Types for representing nutation computation results.

Traits

IERS2010FundamentalArgs

Fundamental arguments from IERS Conventions (2010).

MHB2000FundamentalArgs

Additional fundamental arguments from the MHB2000 nutation model.