earths 0.0.3

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 J2000EPOCH: f64 = 2451545.0;
pub const J1950EPOCH: f64 = 2433282.5;
pub const MJDOFFSET: f64 = 2400000.5;
pub struct Epoch {
    pub juliandate: f64,
}
impl Epoch {
    pub fn j2000() -> Self {
        Self {
            juliandate: J2000EPOCH,
        }
    }
    pub fn fromjd(jd: f64) -> Self {
        Self { juliandate: jd }
    }
    pub fn frommjd(mjd: f64) -> Self {
        Self {
            juliandate: mjd + MJDOFFSET,
        }
    }
    pub fn tomjd(&self) -> f64 {
        self.juliandate - MJDOFFSET
    }
    pub fn centuriessincej2000(&self) -> f64 {
        (self.juliandate - J2000EPOCH) / 36525.0
    }
    pub fn dayssincej2000(&self) -> f64 {
        self.juliandate - J2000EPOCH
    }
    pub fn gmstdegrees(&self) -> f64 {
        let t = self.centuriessincej2000();
        let gmst = 280.46061837 + 360.98564736629 * self.dayssincej2000() + 0.000387933 * t * t
            - t * t * t / 38710000.0;
        let omegarad = (125.04452 - 1934.136261 * t).to_radians();
        let lrad = (280.4665 + 36000.7698 * t).to_radians();
        let lprad = (218.3165 + 481267.8813 * t).to_radians();
        let deltapsiarcsec =
            -17.20 * omegarad.sin() - 1.32 * (2.0 * lrad).sin() - 0.23 * (2.0 * lprad).sin()
                + 0.21 * (2.0 * omegarad).sin();
        let obliquitydeg = 23.4393 - 0.013 * t;
        let eqequinox = deltapsiarcsec / 3600.0 * obliquitydeg.to_radians().cos();
        (gmst + eqequinox) % 360.0
    }
    pub fn advancedays(&mut self, days: f64) {
        self.juliandate += days;
    }
    pub fn advanceseconds(&mut self, seconds: f64) {
        self.juliandate += seconds / super::calendar::SECONDSPERDAY;
    }
}