21 lines
706 B
Rust
21 lines
706 B
Rust
use chrono::{DateTime, Utc};
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/// Compute Julian Date from a UTC datetime.
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pub fn julian_date(dt: DateTime<Utc>) -> f64 {
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let unix_seconds = dt.timestamp() as f64;
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// J2000.0 epoch is 2000-01-01 12:00:00 UTC = Unix 946728000
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// JD of Unix epoch 0 = 2440587.5
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unix_seconds / 86400.0 + 2440587.5
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}
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/// Compute Local Sidereal Time in degrees [0, 360).
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/// Uses IAU formula via Julian Date and observer longitude.
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pub fn local_sidereal_time(jd: f64, lon_deg: f64) -> f64 {
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// Days since J2000.0
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let d = jd - 2451545.0;
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// Greenwich Mean Sidereal Time in degrees
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let gmst_deg = 280.46061837 + 360.98564736629 * d;
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let lst = (gmst_deg + lon_deg).rem_euclid(360.0);
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lst
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}
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