earths 0.0.1

High-fidelity Earth simulation engine — orbit, atmosphere, geology, hydrology, biosphere, terrain, lighting, rendering, satellites, and temporal systems with full scientific coupling
Documentation 
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pub const J2000_EPOCH: f64 = 2451545.0;
pub const J1950_EPOCH: f64 = 2433282.5;
pub const MJD_OFFSET: f64 = 2400000.5;
pub struct Epoch {
    pub julian_date: f64,
}
impl Epoch {
    pub fn j2000() -> Self {
        Self {
            julian_date: J2000_EPOCH,
        }
    }
    pub fn from_jd(jd: f64) -> Self {
        Self { julian_date: jd }
    }
    pub fn from_mjd(mjd: f64) -> Self {
        Self {
            julian_date: mjd + MJD_OFFSET,
        }
    }
    pub fn to_mjd(&self) -> f64 {
        self.julian_date - MJD_OFFSET
    }
    pub fn centuries_since_j2000(&self) -> f64 {
        (self.julian_date - J2000_EPOCH) / 36525.0
    }
    pub fn days_since_j2000(&self) -> f64 {
        self.julian_date - J2000_EPOCH
    }
    pub fn gmst_degrees(&self) -> f64 {
        let t = self.centuries_since_j2000();
        let gmst =
            280.460_618_37 + 360.985_647_366_29 * self.days_since_j2000() + 0.000_387_933 * t * t
                - t * t * t / 38_710_000.0;
        let omega_rad = (125.04452 - 1934.136261 * t).to_radians();
        let l_rad = (280.4665 + 36000.7698 * t).to_radians();
        let lp_rad = (218.3165 + 481267.8813 * t).to_radians();
        let delta_psi_arcsec =
            -17.20 * omega_rad.sin() - 1.32 * (2.0 * l_rad).sin() - 0.23 * (2.0 * lp_rad).sin()
                + 0.21 * (2.0 * omega_rad).sin();
        let obliquity_deg = 23.4393 - 0.013 * t;
        let eq_equinox = delta_psi_arcsec / 3600.0 * obliquity_deg.to_radians().cos();
        (gmst + eq_equinox) % 360.0
    }
    pub fn advance_days(&mut self, days: f64) {
        self.julian_date += days;
    }
    pub fn advance_seconds(&mut self, seconds: f64) {
        self.julian_date += seconds / super::calendar::SECONDS_PER_DAY;
    }
}