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Module coordinates

celestial_core::cio

Module coordinates 

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CIP (Celestial Intermediate Pole) coordinates for the IAU 2000/2006 precession-nutation model.

The Celestial Intermediate Pole defines the axis around which Earth rotates in the Celestial Intermediate Reference System (CIRS). Its position relative to the GCRS is described by two small angles X and Y, which encode the combined effects of precession and nutation.

§When to use this

CIP coordinates are needed when:

  • Converting between GCRS (geocentric celestial) and CIRS (intermediate) frames
  • Computing Earth Rotation Angle for sidereal time
  • Implementing the full IAU 2000/2006 transformation chain

For most high-precision applications, you’ll extract CIP coordinates from a precession-nutation matrix rather than computing them directly.

§Coordinate ranges

X and Y are stored in radians. Current values are on the order of 10^-7 radians (~0.02 arcseconds). The validation threshold of 0.2 radians (~11 degrees) catches obviously invalid matrices while allowing for long-term secular drift.

Structs§

CipCoordinates
Position of the Celestial Intermediate Pole in the GCRS.