Astronomical Applications Department, U.S. Naval Observatory NOVAS 2006 Overview Page 1
NOVAS Changes 2006
The differences between NOVAS F2.9c and NOVAS F3.0d are:
(1) P03 precession is implemented in F3.0d. This affects PRECES, SIDTIM, and ETILT.
NOVAS uses, in PRECES, the canonical 4-angle version of P03. (Formulas 5.7-5.9 in
Circular 179; or Capitaine, et al. 2003, A&A 412, 567, section 7.2; or Hilton et al. 2006,
precession WG report, Celest. Mech. Dyn. Astr. 94, 351.)
(2) The reference points "Celestial Ephemeris Origin (CEO)" and "Terrestrial Ephemeris
Origin (TEO)" are now referred to as the "Celestial Intermediate Origin (CIO)" and
"Terrestrial Intermediate Origin (TIO)", as recommended by the IAU Working Group on
Nomenclature for Fundamental Astronomy. All subroutine names and variable names
containing "CEO" or "TEO" have been changed to "CIO" and "TIO", respectively. This
affected about 100 items. This includes the name of the file of external CIO coordinates,
which is now CIO_RA.TXT.
(3) Subroutine EQECL for equatorial to ecliptic conversion has been divided up
internally although its calling sequence has not been changed. EQECL works on
spherical coordinates (RA & Dec to ecliptic long & lat) although internally it uses a
vector rotation. The vector rotation was split off into a new, separate subroutine called
EQEC, so that vectors can be converted. There is also now the reciprocal subroutine
ECEQ.
(4) Within SOLSYS, the call to the JPL ephemeris-access routine has been changed from
the single-argument JD call to the double-argument JD call -- that is, from PLEPH to
DPLEPH. The way SOLSYS now works is that if you give it a full JD, it just splits the
integer part from the fractional part and sends these to DPLEPH separately. In this case
the result is the same as a call to PLEPH with the JD in one piece. But, there is now a
little bit of code so that if in a subsequent call to SOLSYS, the JD is between -1 and +1,
SOLSYS will interpret it as a fraction of a day to be used with the integral part of the JD
from a previous call. This way there is no effect on existing applications that directly use
SOLSYS, but it provides a higher-precision option if two calls in succession are used in
this way. The way to test whether SOLSYS can use split JDs is to check on whether the
value of IDSS(`JD') is 1 or 2, with 2 meaning that Julian dates can be split between
successive calls. This means that IDSS has also been modified for this option.
(5) LITTIM has been modified to use the split-JD option in SOLSYS when available.
(6) A new subroutine, EQXRA has been added that evaluates the "Equation of the
Origins" from an analytical expression. The expression is simply everything other than
the first (fast) term in sidereal time (i.e., the non-ERA part) that is, the accumulated
precession and nutation in RA. This is comprised of the precession-in-RA polynomial
plus the equation of the equinoxes, the latter including the "complementary terms".
SIDTIM was modified to call EQXRA to compute all of that.
