The time scale

The time scale in these formulae are counted in days. Hours, minutes, seconds are expressed as fractions of a day. Day 0.0 occurs at 2000 Jan 0.0 UT (or 1999 Dec 31, 0:00 UT). This "day number" d is computed as follows (y=year, m=month, D=date, UT=UT in hours+decimals):

d = 367*y - 7 * ( y + (m+9)/12 ) / 4 + 275*m/9 + D - 730530

Note that ALL divisions here should be INTEGER divisions. In Pascal, use "div" instead of "/", in MS-Basic, use "\" instead of "/". In Fortran, C and C++ "/" can be used if both y and m are integers. Finally, include the time of the day, by adding:

d = d + UT/24.0 (this is a floating-point division)