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Astronomical Applications Department, U.S. Naval Observatory - novas c 2 doc (Page 13)

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Astronomical Applications Department, U.S. Naval Observatory - novas c 2 doc
13
4.0 Important Functions in NOVAS-C
4.1
APP_STAR
short int app_star (double tjd, body *earth, cat_entry *star,
double *ra, double *dec)
PURPOSE:
Computes the apparent place of a star at date 'tjd', given its
mean place, proper motion, parallax, and radial velocity for
J2000.0.
INPUT
ARGUMENTS:
tjd (double)
TT (or TDT) Julian date for apparent place.
*earth (struct body)
Pointer to structure containing the body designation for the
Earth (defined in novas.h).
*star (struct cat_entry)
Pointer to catalog entry structure containing J2000.0 catalog
data with FK5-style units (defined in novas.h).
OUTPUT
ARGUMENTS:
*ra (double)
Apparent right ascension in hours, referred to true equator
and equinox of date 'tjd'.
*dec (double)
Apparent declination in degrees, referred to true equator
and equinox of date 'tjd'.
RETURNED
VALUE:
(short int)
0...Everything OK.
>0...Error code from function 'solarsystem'.
Discussion:
This function computes the apparent place of a star. The word "star" as used here
refers to any object outside the solar system. If the values of
promora
,
promodec
,
parlax
, or
radvel
within structure
star
are unknown (or zero within the errors of
measurement), the calling program should set them to zero. For extragalactic objects,
these input values should be set to zero. The user's choice of the version of function
solarsystem determines the value of the argument
earth
that the calling program must
supply to app_star.
"Loose" catalog data can be assembled into a structure of type cat
_entry
by using
function make_cat_entry.

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