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Astronomy

The AstronomyExtensions class provides extension methods for astronomical calculations: distance conversions, Julian date, sidereal time, and horizontal ↔ equatorial coordinate transforms.

📏 Distance Conversions​

Convert between light-years, parsecs, and astronomical units:

double pc = 4.37.LightYearsToParsecs();      // Proxima Centauri ≈ 1.34 pc
double ly = 1.0.ParsecsToLightYears();        // 1 pc ≈ 3.26 ly
double au = 1.0.LightYearsToAU();             // 1 ly ≈ 63241 AU
double au2 = 1.0.ParsecsToAU();               // 1 pc ≈ 206265 AU

📅 Julian Date​

Compute Julian Date and Julian centuries since J2000.0:

var utc = new DateTime(2024, 6, 15, 21, 0, 0, DateTimeKind.Utc);

double jd = utc.ToJulianDate();               // Julian Date
double T  = utc.JulianCenturiesSinceJ2000();  // centuries since J2000.0

⏱️ Sidereal Time​

Compute Greenwich and local sidereal time from UTC, or from local time with time zone:

var utc = new DateTime(2024, 6, 15, 21, 0, 0, DateTimeKind.Utc);

double gmst = utc.GreenwichMeanSiderealTimeHours();       // GMST in hours
double gmstDeg = utc.GreenwichMeanSiderealTimeDegrees();   // GMST in degrees

// Local sidereal time (Stockholm: 18.07° E)
double lmst = utc.LocalMeanSiderealTimeHours(18.07);

// From local time + time zone + longitude
var local = new DateTime(2024, 6, 15, 23, 0, 0);
double lst = local.LocalSiderealTimeFromLocal(
    utcOffsetHours: 2.0,       // UTC+2 (CEST)
    longitudeDegrees: 18.07);  // Stockholm

⬆️ Horizontal → Equatorial (Altitude/Azimuth → RA/Dec)​

Convert what you observe (altitude, azimuth) to sky coordinates (right ascension, declination):

// Using explicit local sidereal time
var (ra, dec) = AstronomyExtensions.HorizontalToEquatorial(
    altitudeDegrees: 45.0,
    azimuthDegrees: 180.0,     // due south
    latitudeDegrees: 51.48,    // London
    localSiderealTimeDegrees: 120.0);

// Using UTC time and longitude (LST computed automatically)
var utc = new DateTime(2024, 3, 20, 22, 0, 0, DateTimeKind.Utc);
var (ra2, dec2) = AstronomyExtensions.HorizontalToEquatorial(
    altitudeDegrees: 45.0,
    azimuthDegrees: 180.0,
    latitudeDegrees: 51.48,
    longitudeDegrees: 0.0,     // Greenwich
    utc: utc);

⬇️ Equatorial → Horizontal (RA/Dec → Altitude/Azimuth)​

Find where a star appears in the sky from your location:

var (alt, az) = AstronomyExtensions.EquatorialToHorizontal(
    rightAscensionDegrees: 200.0,
    declinationDegrees: 30.0,
    latitudeDegrees: 59.33,    // Stockholm
    localSiderealTimeDegrees: 120.0);

// Or with UTC + position
var (alt2, az2) = AstronomyExtensions.EquatorialToHorizontal(
    rightAscensionDegrees: 200.0,
    declinationDegrees: 30.0,
    latitudeDegrees: 59.33,
    longitudeDegrees: 18.07,
    utc: utc);

📐 Angle Helpers​

Convert between common astronomical angle formats:

// Right ascension: hours/min/sec ↔ degrees
double deg = AstronomyExtensions.RightAscensionToDegrees(6, 30, 0);  // → 97.5°
var (h, m, s) = AstronomyExtensions.DegreesToRightAscension(97.5);    // → (6, 30, 0.0)

// Declination: degrees/arcmin/arcsec → decimal degrees
double dec = AstronomyExtensions.DeclinationToDegrees(-16, 42, 58);   // → -16.7161°