mean anomaly where: M is the solar mean anomaly used in the next three equations. Equation of the center where: C is the Equation of the center value needed to calculate lambda (see next equation). 1.9148 is the coefficient of the Equation of the Center for the planet the observer is on (in this case, Earth) Ecliptic longitude where: λ is the ecliptic longitude. 102.9372 is a value for the argument of perihelion. Solar transit where: Jtransit is the Julian date for the local true solar transit (or solar noon). 2451545.0 is noon of the equivalent Julian year reference. is a simplified version of the equation of time. The coefficients are fractional days. Declination of the Sun where: is the declination of the sun. 23.44° is Earth's maximum axial tilt toward the sun Hour angle This is the equation from above with corrections for atmospherical refraction and solar disc diameter. where: ωo is the hour angle from the observer's meridian; is the north latitude of the observer (north is positive, south is negative) on the Earth. For observations on a sea horizon needing an elevation-of-observer correction, add , or to the −0.83° in the numerator's sine term. This corrects for both apparent dip and terrestrial refraction. For example, for an observer at 10,000 feet, add (−115°/60) or about −1.92° to −0.83°. Calculate sunrise and sunset where: Jrise is the actual Julian date of sunrise; Jset is the actual Julian date of sunset. See also Day length Equation of time References External links Sunrise, sunset, or sun position for any location – U.S. only Sunrise, sunset and day length for any location – Worldwide Rise/Set/Transit/Twilight Data – U.S. only Astronomical Information Center Converting Between Julian Dates and Gregorian Calendar Dates Approximate Solar Coordinates Algorithms for Computing Astronomical Phenomena Astronomy Answers: Position of the Sun A Simple Expression for the Equation of Time The Equation of Time Equation of Time Long-Term Almanac for Sun, Moon, and Polaris V1.11 Evaluating the Effectiveness of Current Atmospheric Refraction Models in Predicting Sunrise and Sunset Times Equations Time in astronomy Dynamics of the Solar System