Month: January 2015


The Standards of Fundamental Astronomy (SOFA) library is a very nice collection of routines that implement various IAU algorithms for fundamental astronomy computations. Versions are available in Fortran and C.  Unfortunately, the Fortran version is written to be of maximum use to astronomers who

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Nonsingular Geopotential Models

The gravitational potential of a non-homogeneous celestial body at radius , latitude , and longitude can be represented in spherical coordinates as: Where is the radius of the body, is the gravitational parameter of the body, and  are spherical harmonic coefficients,

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Julian Date

Julian date is a count of the number of days since noon on January 1, 4713 BC in the proleptic Julian calendar.  This epoch was chosen by Joseph Scaliger in 1583 as the start of the “Julian Period”: a 7,980

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