skymath

Rust library of planning-grade astronomy math for astrophotography tooling.

• Angles — typed Angle (degrees, radians, hours, arcminutes, arcseconds), normalization helpers, exact conversion constants.
• Equatorial coordinates — validated RA/Dec with epoch (J2000 or of-date); sexagesimal parsing in strict and lenient modes, and sexagesimal formatting.
• Spherical geometry — great-circle separation, position angle, tangent-plane offsets and their inverse (offset applied to a coordinate).
• Precession — IAU-1976 conversion between J2000 and equinox-of-date.
• Coordinate frames — equatorial ↔ galactic and equatorial ↔ ecliptic.
• Time — MJD/JD ↔ calendar conversions, FITS DATE-OBS parsing and formatting, Julian epoch from a date, Greenwich and local sidereal time.
• Observer-local quantities — observer Location (with sexagesimal parsing), hour angle, alt-azimuth transforms, airmass, atmospheric refraction, parallactic angle, and transit / altitude-crossing times.
• Sun & Moon — solar and lunar positions (geocentric and topocentric), twilight times (civil / nautical / astronomical, with typed polar-night and midnight-sun outcomes), moonrise/set, lunar separation from a target, Moon illumination and phase angle, and the moon-avoidance Lorentzian criterion.
• Constellations — which of the 88 IAU constellations contains a coordinate (Roman 1987 boundary table at B1875.0), as a typed value with official abbreviations ("UMi") and Latin names ("Ursa Minor", "Boötes").

Precision is planning-grade (≈1 arcminute) throughout: suitable for framing, scheduling, and session planning, not for telescope pointing or astrometry. Apparent-place corrections (nutation, aberration, proper motion) are out of scope by design.

Usage

use skymath::{alt_az, altitude_crossings, separation, Angle, CrossingOutcome,
              Equatorial, Location, ParseMode};
use time::OffsetDateTime;

fn main() -> skymath::Result<()> {
    let site = Location::parse("+52 05 32", "+004 18 27", 6.0)?;
    let m31 = Equatorial::parse_j2000("00:42:44.3", "+41:16:09", ParseMode::Strict)?;

    let now = OffsetDateTime::now_utc();
    let h = alt_az(m31, now, &site);
    println!("M31: alt {:.1}°, az {:.1}°", h.altitude.degrees(), h.azimuth.degrees());

    match altitude_crossings(m31, Angle::from_degrees(30.0), now, &site) {
        CrossingOutcome::Crosses { rise, set } => println!("above 30°: {rise} → {set}"),
        outcome => println!("{outcome:?}"),
    }
    Ok(())
}

cargo run --example plan_night walks the full planning flow (site + target parsing, precession to tonight, sidereal time, airmass, parallactic angle, transit and window). Enable the serde feature for Serialize/Deserialize derives on all public types.

Instants are time crate types; functions taking an OffsetDateTime fold the offset in internally, so passing local civil time cannot skew results.

License

Licensed under the Apache License, Version 2.0.