Calculation accuracy
Namespace:
ASCOM.Astrometry
Assembly:
ASCOM.Astrometry (in ASCOM.Astrometry.dll) Version: 3351c4f3fa64146a7efd5b51ed4591e32a0a5484
Syntax Public Enumeration Accuracy
public enum class Accuracy
Members
| Member name | Value | Description |
---|
| Full | 0 |
Full accuracy
|
| Reduced | 1 |
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