Spline-Based Formulas for the Determination of Equation of Time and Declination Angle

This paper presents new approximation formulas for the determination of the equation of time and declination angle. The proposed approach is based on the cubic spline interpolation techniques defined for sixteen or twenty chosen knots over the whole year. The results obtained by the proposed formulas for both equation of time and declination angle show marked improvements in terms of speed and sum of squared errors and maximum absolute error over the whole year in comparison with other five existing methods for analytical evaluation of equation of time and two existing methods for analytical evaluation of declination angle.