Function getTime

src/utils/time.ts:140–211

(isSunrise: boolean)

    const lnHour = longitude / 15;

    function getTime(isSunrise: boolean) {
        const t = dayOfYear + (((isSunrise ? 6 : 18) - lnHour) / 24);

        // calculate the Sun's mean anomaly
        const M = (0.9856 * t) - 3.289;

        // calculate the Sun's true longitude
        let L = M + (1.916 * Math.sin(M * D2R)) + (0.020 * Math.sin(2 * M * D2R)) + 282.634;
        if (L > 360) {
            L -= 360;
        } else if (L < 0) {
            L += 360;
        }

        // calculate the Sun's right ascension
        let RA = R2D * Math.atan(0.91764 * Math.tan(L * D2R));
        if (RA > 360) {
            RA -= 360;
        } else if (RA < 0) {
            RA += 360;
        }

        // right ascension value needs to be in the same qua
        const Lquadrant = (Math.floor(L / (90))) * 90;
        const RAquadrant = (Math.floor(RA / 90)) * 90;
        RA += (Lquadrant - RAquadrant);

        // right ascension value needs to be converted into hours
        RA /= 15;

        // calculate the Sun's declination
        const sinDec = 0.39782 * Math.sin(L * D2R);
        const cosDec = Math.cos(Math.asin(sinDec));

        // calculate the Sun's local hour angle
        const cosH = (Math.cos(zenith * D2R) - (sinDec * Math.sin(latitude * D2R))) / (cosDec * Math.cos(latitude * D2R));
        if (cosH > 1) {
            // always night
            return {
                alwaysDay: false,
                alwaysNight: true,
                time: 0,
            };
        } else if (cosH < -1) {
            // always day
            return {
                alwaysDay: true,
                alwaysNight: false,
                time: 0,
            };
        }

        const H = (isSunrise ? (360 - R2D * Math.acos(cosH)) : (R2D * Math.acos(cosH))) / 15;

        // calculate local mean time of rising/setting
        const T = H + RA - (0.06571 * t) - 6.622;

        // adjust back to UTC