celestial-coords

Type-safe astronomical coordinate transformations between reference frames.

Pure Rust implementation of coordinate frame transformations with full aberration, light deflection, and Earth orientation support. Each frame is a distinct type to prevent accidental mixing. ICRS serves as the pivot for all transformations.

Installation

[dependencies]
celestial-coords = "0.1"

Coordinate Frames

Modules

Example

use celestial_coords::{ICRSPosition, GalacticPosition, Distance};
use celestial_coords::transforms::CoordinateFrame;
use celestial_time::TT;

// Create a position in ICRS (catalog coordinates)
let sirius = ICRSPosition::from_hours_degrees(6.752, -16.716)?;

// Transform to Galactic coordinates
let epoch = TT::j2000();
let galactic = sirius.to_galactic(&epoch)?;
println!("l = {:.2}°, b = {:.2}°", galactic.longitude().degrees(), galactic.latitude().degrees());

// With distance (parallax-derived)
let distance = Distance::from_parallax_milliarcsec(379.21)?;
let proxima = ICRSPosition::from_degrees_with_distance(217.42, -62.68, distance)?;
println!("Distance: {:.2} pc", proxima.distance().unwrap().parsecs());

Transformation Chain

ICRS (catalog)
  ↓ frame bias + precession + nutation (IAU 2006A)
  ↓ stellar aberration (~20.5")
  ↓ gravitational light deflection (~1.75" max)
CIRS (geocentric apparent)
  ↓ Earth rotation (GAST)
TIRS
  ↓ polar motion (EOP)
ITRS (terrestrial)

All transformations use ICRS as the pivot frame. The CoordinateFrame trait provides:

pub trait CoordinateFrame: Sized {
    fn to_icrs(&self, epoch: &TT) -> CoordResult<ICRSPosition>;
    fn from_icrs(icrs: &ICRSPosition, epoch: &TT) -> CoordResult<Self>;
}

Earth Orientation Parameters

Required for CIRS to ITRS transformations (polar motion, UT1-UTC):

use celestial_coords::eop::{EopManager, EopBuilder};

// Load embedded baseline data (1962-present)
let mut eop = EopBuilder::default().build()?;

// Get parameters for a specific MJD
let params = eop.get(60000.0)?;
println!("UT1-UTC = {:.4} s", params.ut1_utc);
println!("Polar motion: x={:.3}\", y={:.3}\"",
    params.x_p * 206264.806,
    params.y_p * 206264.806);

Features

• serde - Serialization for coordinate types and EOP records
• eop-download - Network download of EOP data (requires serde)

Topocentric Observations

use celestial_coords::{TopocentricPosition, Distance};
use celestial_core::{Angle, Location};
use celestial_time::TT;

let observer = Location::from_degrees(19.8283, -155.4783, 4145.0)?; // Keck
let epoch = TT::j2000();

let moon_distance = Distance::from_kilometers(384400.0)?;
let moon = TopocentricPosition::with_distance(
    Angle::from_degrees(180.0),
    Angle::from_degrees(45.0),
    observer,
    epoch,
    moon_distance,
)?;

// Airmass (Rozenberg formula)
println!("Airmass: {:.2}", moon.air_mass());

// Atmospheric refraction (standard conditions)
let refraction = moon.atmospheric_refraction(1013.25, 15.0, 0.5, 0.574);
println!("Refraction: {:.1}\"", refraction.arcseconds());

// Diurnal parallax
let parallax = moon.diurnal_parallax().unwrap();
println!("Parallax: {:.1}'", parallax.arcminutes());

Solar and Lunar Coordinates

use celestial_coords::solar::{compute_solar_orientation, carrington_rotation_number};
use celestial_coords::lunar::compute_optical_libration;
use celestial_time::TT;

let epoch = TT::j2000();

// Solar orientation
let solar = compute_solar_orientation(&epoch);
println!("B0 = {:.2}°", solar.b0.degrees());
println!("L0 = {:.2}°", solar.l0.degrees());
println!("Carrington rotation: {}", carrington_rotation_number(&epoch));

// Lunar libration
let (lib_lon, lib_lat) = compute_optical_libration(&epoch);
println!("Libration: lon={:.2}°, lat={:.2}°", lib_lon.degrees(), lib_lat.degrees());

License

Licensed under either of:

• Apache License, Version 2.0
• MIT License

Contributing

See the repository for contribution guidelines.