/**
* Calculates all sun-related important times
* depending on time of year and location
* @param Location Location to be used in calculation
* @param Basic NMEA_INFO for current date
* @param Calculated DERIVED_INFO (not yet used)
* @param TimeZone The timezone
* @return Sunset time
*/
void
SunEphemeris::CalcSunTimes(const GeoPoint &Location,
const BrokenDateTime &date_time,
const fixed TimeZone)
{
fixed DaysToJ2000 = FNday(date_time);
Angle L = GetMeanSunLongitude(DaysToJ2000);
// Use GetEclipticLongitude to find the ecliptic longitude of the Sun
Angle Lambda = GetEclipticLongitude(DaysToJ2000, L);
// Obliquity of the ecliptic
Angle Obliquity = Angle::degrees(fixed(23.439) - fixed(.0000004) * DaysToJ2000);
// Find the RA and DEC of the Sun
Angle Alpha = Angle::radians(atan2(Obliquity.cos() * Lambda.sin(), Lambda.cos()));
Angle Delta = Angle::radians(asin(Obliquity.sin() * Lambda.sin()));
// Find the Equation of Time in minutes
// Correction suggested by David Smith
fixed LL = (L - Alpha).value_radians();
if (L.value_radians() < fixed_pi)
LL += fixed_two_pi;
fixed equation = fixed(1440) * (fixed_one - LL / fixed_two_pi);
Angle HourAngle = GetHourAngle(Location.Latitude, Delta);
Angle HourAngleTwilight = GetHourAngleTwilight(Location.Latitude, Delta);
// length of twilight in hours
fixed TwilightHours = (HourAngleTwilight - HourAngle).value_hours();
// Conversion of angle to hours and minutes
DayLength = HourAngle.value_hours() * fixed_two;
if (DayLength < fixed(0.0001))
// arctic winter
DayLength = fixed_zero;
TimeOfSunRise = fixed(12) - HourAngle.value_hours() + TimeZone
- Location.Longitude.value_degrees() / 15 + equation / 60;
if (TimeOfSunRise > fixed(24))
TimeOfSunRise -= fixed(24);
TimeOfSunSet = TimeOfSunRise + DayLength;
TimeOfNoon = TimeOfSunRise + HourAngle.value_hours();
// morning twilight begin
MorningTwilight = TimeOfSunRise - TwilightHours;
// evening twilight end
EveningTwilight = TimeOfSunSet + TwilightHours;
}
Angle
SunEphemeris::CalcAzimuth(const GeoPoint &location,
const BrokenDateTime &date_time,
const fixed time_zone)
{
assert(date_time.Plausible());
fixed days_to_j2000 = FNday(date_time);
Angle l = GetMeanSunLongitude(days_to_j2000);
// Use GetEclipticLongitude to find the ecliptic longitude of the Sun
Angle lambda = GetEclipticLongitude(days_to_j2000, l);
// Obliquity of the ecliptic
Angle obliquity = Angle::Degrees(fixed(23.439) - fixed(.0000004) * days_to_j2000);
// Find the DEC of the Sun
Angle delta = Angle::asin(obliquity.sin() * lambda.sin());
return CalculateAzimuth(location, date_time, time_zone, delta);
}
SunEphemeris::Result
SunEphemeris::CalcSunTimes(const GeoPoint &location,
const BrokenDateTime &date_time,
const fixed time_zone)
{
Result result;
assert(date_time.Plausible());
fixed days_to_j2000 = FNday(date_time);
Angle l = GetMeanSunLongitude(days_to_j2000);
// Use GetEclipticLongitude to find the ecliptic longitude of the Sun
Angle lambda = GetEclipticLongitude(days_to_j2000, l);
// Obliquity of the ecliptic
Angle obliquity = Angle::Degrees(fixed(23.439) - fixed(.0000004) * days_to_j2000);
// Find the RA and DEC of the Sun
Angle alpha = Angle::FromXY(lambda.cos(), obliquity.cos() * lambda.sin());
Angle delta = Angle::asin(obliquity.sin() * lambda.sin());
// Find the Equation of Time in minutes
// Correction suggested by David Smith
fixed ll = (l - alpha).Radians();
if (l.Radians() < fixed_pi)
ll += fixed_two_pi;
fixed equation = fixed(1440) * (fixed(1) - ll / fixed_two_pi);
Angle hour_angle = GetHourAngle(location.latitude, delta);
Angle hour_angle_twilight = GetHourAngleTwilight(location.latitude, delta);
result.azimuth = CalculateAzimuth(location, date_time, time_zone, delta);
// length of twilight in hours
fixed twilight_hours = (hour_angle_twilight - hour_angle).Hours();
// Conversion of angle to hours and minutes
result.day_length = Double(hour_angle.Hours());
if (result.day_length < fixed(0.0001))
// arctic winter
result.day_length = fixed(0);
result.time_of_sunrise = fixed(12) - hour_angle.Hours() + time_zone
- location.longitude.Degrees() / 15 + equation / 60;
if (result.time_of_sunrise > fixed(24))
result.time_of_sunrise -= fixed(24);
result.time_of_sunset = result.time_of_sunrise + result.day_length;
result.time_of_noon = result.time_of_sunrise + hour_angle.Hours();
// morning twilight begin
result.morning_twilight = result.time_of_sunrise - twilight_hours;
// evening twilight end
result.evening_twilight = result.time_of_sunset + twilight_hours;
return result;
}
