Calculate sunrise and sunset times using geographic coordinates and date.

sunrise-sunset.php

<?php

/**
 * Check whether the given year is a leap year.
 */
function isLeapYear(int $year): bool
{
    return $year % 400 === 0
        || ($year % 4 === 0 && $year % 100 !== 0);
}

/**
 * Convert a date to the day number within the year.
 *
 * Examples:
 * January 1  = 1
 * January 31 = 31
 * February 1 = 32
 */
function dayOfYear(int $year, int $month, int $day): int
{
    $daysInMonths = [
        31, 28, 31, 30, 31, 30,
        31, 31, 30, 31, 30, 31,
    ];

    if (isLeapYear($year)) {
        $daysInMonths[1] = 29;
    }

    $result = $day;

    for ($i = 0; $i < $month - 1; $i++) {
        $result += $daysInMonths[$i];
    }

    return $result;
}

/**
 * Convert decimal hours to HH:MM:SS.
 *
 * Example:
 * 5.5 -> 05:30:00
 */
function hoursToTime(float $hours): string
{
    $hours = fmod($hours, 24);

    if ($hours < 0) {
        $hours += 24;
    }

    $totalSeconds = (int) round($hours * 3600) % 86400;

    $hour = intdiv($totalSeconds, 3600);
    $minute = intdiv($totalSeconds % 3600, 60);
    $second = $totalSeconds % 60;

    return sprintf('%02d:%02d:%02d', $hour, $minute, $second);
}

/**
 * Calculate sunrise and sunset times.
 */
function calculateSun(
    int $year,
    int $month,
    int $day,
    float $latitude,
    float $longitude,
    float $timezone,
): array {
    // 1. Day of the year
    $dayOfYear = dayOfYear($year, $month, $day);

    // 2. Fractional year angle, in radians
    $gamma = (2 * M_PI / 365) * ($dayOfYear - 1);

    // 3. Difference between apparent solar time and clock time, in minutes
    $equationOfTime = 229.18 * (
        0.000075
        + 0.001868 * cos($gamma)
        - 0.032077 * sin($gamma)
        - 0.014615 * cos(2 * $gamma)
        - 0.040849 * sin(2 * $gamma)
    );

    // 4. Solar declination, in radians
    $declination =
        0.006918
        - 0.399912 * cos($gamma)
        + 0.070257 * sin($gamma)
        - 0.006758 * cos(2 * $gamma)
        + 0.000907 * sin(2 * $gamma)
        - 0.002697 * cos(3 * $gamma)
        + 0.001480 * sin(3 * $gamma);

    // 5. Convert latitude to radians
    $latitudeRad = deg2rad($latitude);

    /**
     * 6. Sunrise / sunset zenith
     *
     * 90°     = geometric horizon
     * 0.266°  = apparent solar radius
     * 0.567°  = atmospheric refraction
     *
     * Total: 90.833°
     */
    $zenith = deg2rad(90.833);

    // 7. Calculate the hour angle at the horizon
    $cosHourAngle =
        cos($zenith) / (cos($latitudeRad) * cos($declination))
        - tan($latitudeRad) * tan($declination);

    // Polar night: the Sun does not rise
    if ($cosHourAngle > 1) {
        return [
            'sunrise' => null,
            'sunset' => null,
            'status' => 'Sun does not rise',
        ];
    }

    // Midnight Sun: the Sun does not set
    if ($cosHourAngle < -1) {
        return [
            'sunrise' => null,
            'sunset' => null,
            'status' => 'Sun does not set',
        ];
    }

    // 8. Convert hour angle from radians to degrees
    $hourAngle = rad2deg(acos($cosHourAngle));

    // 9. Solar peak time, in minutes from midnight
    $solarPeakMinutes =
        720
        - 4 * $longitude
        - $equationOfTime
        + $timezone * 60;

    /**
     * Earth rotates 360° in 24 hours:
     *
     * 360 / 24 = 15° per hour
     * 1° = 4 minutes
     */
    $offsetMinutes = $hourAngle * 4;

    // 10. Sunrise and sunset times
    $sunriseMinutes = $solarPeakMinutes - $offsetMinutes;
    $sunsetMinutes = $solarPeakMinutes + $offsetMinutes;

    return [
        'sunrise' => hoursToTime($sunriseMinutes / 60),
        'sunset' => hoursToTime($sunsetMinutes / 60),

        // Debug values
        'day_of_year' => $dayOfYear,
        'equation_of_time' => $equationOfTime,
        'declination_deg' => rad2deg($declination),
        'solar_peak' => hoursToTime($solarPeakMinutes / 60),

        'status' => 'OK',
    ];
}


// ------------------------------------------------------
// Example: Tashkent, August 19, 2026
// ------------------------------------------------------

$result = calculateSun(
    year: 2026,
    month: 8,
    day: 19,
    latitude: 41.2995,
    longitude: 69.2401,
    timezone: 5,
);

echo "Sunrise:    {$result['sunrise']}" . PHP_EOL;
echo "Sunset:     {$result['sunset']}" . PHP_EOL;
echo PHP_EOL;

echo "Solar peak: {$result['solar_peak']}" . PHP_EOL;
echo "Declination: {$result['declination_deg']}°" . PHP_EOL;
echo "Time difference: {$result['equation_of_time']} min" . PHP_EOL;