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Accuracy Enumeration

Calculation accuracy

Namespace:  ASCOM.Astrometry
Assembly:  ASCOM.Astrometry (in ASCOM.Astrometry.dll) Version: 3c9121baba46811fe6e53a58a05935662261416d
Syntax
public enum Accuracy
Members
  Member nameValueDescription
Full0 Full accuracy
Reduced1 Reduced accuracy
Remarks
In full-accuracy mode,
  • nutation calculations use the IAU 2000A model [iau2000a, nutation_angles];
  • gravitational deflection is calculated using three bodies: Sun, Jupiter, and Saturn [grav_def];
  • the equation of the equinoxes includes the entire series when computing the “complementary terms" [ee_ct];
  • geocentric positions of solar system bodies are adjusted for light travel time using split, or two-part, Julian dates in calls to ephemeris and iterate with a convergence tolerance of 10-12 days [light_time, ephemeris];
  • ephemeris calls the appropriate solar system ephemeris using split, or two-part, Julian dates primarily to support light-time calculations [ephemeris, solarsystem_hp, light_time].

In reduced-accuracy mode,

  • nutation calculations use the 2000K model, which is the default for this mode;
  • gravitational deflection is calculated using only one body, the Sun [grav_def];
  • the equation of the equinoxes excludes terms smaller than 2 micro arc seconds when computing the "complementary terms" [ee_ct];
  • geocentric positions of solar system bodies are adjusted for light travel time using single-value Julian dates in calls to ephemeris and iterate with a convergence tolerance of 10-9 days [light-time, ephemeris, solar system];
  • ephemeris calls the appropriate solar system ephemeris using single-value Julian dates [ephemeris, solar system].

In full-accuracy mode, the IAU 2000A nutation series (1,365 terms) is used [iau2000a]. Evaluating the series for nutation is usually the main computational burden in NOVAS, so using reduced-accuracy mode improves execution time, often noticeably. In reduced-accuracy mode, the NOVAS 2000K nutation series (488 terms) is used by default [nu2000k]. This mode can be used when the accuracy requirements are not better than 0.1 milliarcsecond for stars or 3.5 milli arc-seconds for solar system bodies. Selecting this approach can reduce the time required for Earth-rotation computations by about two-thirds.

See Also