Here is a collection of Functions relating to astronomy from Stargazing.net.
Can't tell who might be interested in the obliquity of the equator given date in days after J2000.0.
See: Astro VBA
Other Curve stuff:
DelphiForFun.org: converting polar coordinates to Cartesian coordinates.
"Students of analytic geometry, (the kind that combines algebra and geometry), often work in one of two coordinate systems: Cartesian or Polar - and frequently must convert from one to the other.
The Cartesian system locates points on a plane by measuring the horizontal and vertical distances from an arbitrary origin to a point. These are usually denoted as a pair of values (X, Y).
The Polar system locates the point by measuring the straight line distance, usually denoted by R, from the origin to the point and the angle of an imaginary line from the origin to the point, θ, (Greek letter Theta), measured counterclockwise from the positive X axis."
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