This component computes the solar declination, which is
the angle between the equatorial plane and the solar beam.
The input signal nDay
is the one-based number of the day, but in seconds.
Hence, during January 1, we should have nDay = 86400
seconds.
Since the effect of using a continuous number rather than an integer is small,
we approximate this so that nDay = 0
at the start of January 1,
and nDay = 86400
at the end of January 1.
A validation with a more detailed calculation can be found at Annex60.BoundaryConditions.SolarGeometry.BaseClasses.Examples.Declination.