Nutation Series Evaluation in NOVAS 3.0
Abstract
This circular describes the computation of nutation in the Naval Observatory Vector Astrometry Software (NOVAS),1 version 3.0. A detailed description of NOVAS 3.0 may be found in USNO Circular 180 (Kaplan et al. 2009),2 which consists of users guides for both the Fortran and C versions. Nutation is a small periodic oscillation of the Earths axis with respect to a space-fixed reference system (inertial space) caused by the torque of the Sun and Moonand to a lesser extent, the other planetson the Earths equatorial bulge. Nutation is usually modeled by lengthy trigonometric series that, when evaluated for a specific date and time, yield the values of two ecliptic angles: the nutation in longitude, , and the nutation in obliquity, . The evaluation of the nutation series is generally the most computationally intensive part of calculating the positions of celestial objects with respect to the traditional celestial coordinate system defined by the true equator and equinox of date. NOVAS provides several nutation series with different numbers of terms, which the user can select depending on the accuracy requirements.
Document Details
- Document Type
- Technical Report
- Publication Date
- Dec 15, 2009
- Accession Number
- AD1112517
Entities
People
- G. H. Kaplan
Organizations
- United States Naval Observatory