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Astronomical Applications Department, U.S. Naval Observatory - NOVAS 2004 Overview (Page 8)

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Astronomical Applications Department, U.S. Naval Observatory - NOVAS 2004 Overview
Changes to NOVAS ­ From Version F2.0 (1998) to Version F2.9 (2004)

New Subroutines
NU2000A ­ from IERS (Wallace), evaluates IAU 2000A nutation series (nutation only).
NU2000K ­ modification of NU2000A, evaluates truncated version of full IAU 2000 A. More
accurate than IAU 2000 B series. Also uses a consistent set of expressions for the fundamental
arguments, those of Simon et al. (1994). Accuracy: about 0.1 mas for , about 0.04 mas for
and sin
EECT2000 ­ from IERS (Wallace), evaluates 34-term series for "complementary terms" in equation of
the equinoxes.
EROT ­ evaluates the Earth rotation angle
FRAME ­ sets up frame tie matrix and transforms vector from dynamical mean J2000.0 system to
ICRS, or vice versa. FRAME implements a first-order matrix with second-order corrections to
the diagonal elements, patterned after what is given in the Hilton and Hohenkerk (2004) A&A
paper. Given the smallness of the angles involved and their uncertainties, this is quite adequate.
PLACE ­ New, general-purpose subroutine for computing apparent, topocentric, virtual, astrometric,
etc., places of stars and planets. All substantive code for performing these calculations has been
moved from APSTAR, TPSTAR, APPLAN, etc., into PLACE. In the call to PLACE, the object
requested is specified by name, using a character argument, e.g., `SUN', `MOON', `JUPITER',
`STAR', etc. The type of place requested is specified by two input codes, one indicating the
location of the observer and the other indicating the coordinate system of the output positions.
APSTAR, TPSTAR, APPLAN, etc., now are just "front-ends" to PLACE.
SETVEC ­ stores the last-computed celestial position vector.
GETVEC ­ allows the user to retrieve the last-computed celestial position as a unit vector.
IDSS ­ returns the planet number of a specified solar system body, to be used in calls to SOLSYS,
APSTAR, APPLAN, etc. Actually a FUNCTION. The solar system body is specified by its name
(all upper case letters) in the character variable that is the single input argument. For example,
IDSS(`EARTH') = 3 (usually). A version of IDSS must now be packaged with each version of
ASTCON ­ provides values of astronomical constants.
SETDT ­ allows user specification of T (=TT­UT1) value in seconds. The T value set here is used
both in SIDTIM and TERCEL and, in certain circumstances, in PLACE.
GETDT ­ retrieves T value (in days) previously specified via SETDT (in seconds).
ICRSEQ ­ transforms ICRS RA & Dec to RA & Dec on mean or true equator of date. For true equator
of date, either the true equinox or the CEO can be specified as the origin of right ascension.
EQECL ­ converts equatorial RA & Dec to ecliptic longitude and latitude (both input and output are
dynamical coordinates, either mean or true).
EQGAL ­ converts ICRS RA & Dec to galactic longitude and latitude.
DLIGHT ­ evaluates the difference in light-time to a star between the solar system barycenter and the

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