SKY(VI)                      9/22/73                      SKY(VI)


     sky - obtain ephemerides




     Sky predicts the apparent locations of the  Sun,  the  Moon,

     the  planets out to Saturn, stars of magnitude at least 2.5,

     and certain other celestial objects including comet Kohoutek

     and  M31.  Sky reads the standard input to obtain a GMT time

     typed on one line with blanks separating year, month number,

     day,  hour,  and  minute; if the year is missing the current

     year is used.  If a blank line is typed the current time  is

     used.   The  program  prints  the  azimuth,  elevation,  and

     magnitude of objects which are  above  the  horizon  at  the

     ephemeris location of Murray Hill at the indicated time.

     Placing a ``1'' input after  the  minute  entry  causes  the

     program  to  print  out  the  Greenwich Sidereal Time at the

     indicated moment and  to  print  for  each  body  its  right

     ascension  and  declination  as  well  as  its  azimuth  and

     elevation.  Also, instead of the magnitude,  the  geocentric

     distance  of  the  body,  in  units  the  program  considers

     convenient,  is  printed.   (For   planets   the   unit   is

     essentially A. U.)

     The magnitudes of Solar System bodies are not calculated and

     are  given  as 0.  The effects of atmospheric extinction are

     not included; the mean  magnitudes  of  variable  stars  are

     marked with ``*''.

     For all bodies, the program takes  into  account  precession

     and  nutation  of  the  equinox,  annual  (but  not diurnal)

     aberration, diurnal parallax, and the proper motion of stars

     (but  not  annual  parallax).   In  no  case  is  refraction


     The program takes into account perturbations  of  the  Earth

     due  to  the  Moon,  Venus, Mars, and Jupiter.  The expected

     accuracies are: for the Sun and other stellar bodies  a  few

     tenths  of seconds of arc; for the Moon (on which particular

     care is lavished) likewise a few tenths of seconds.  For the

     Sun,  Moon  and  stars the accuracy is sufficient to predict

     the circumstances of eclipses and occultations to  within  a

     few  seconds  of  time.   The  planets may be off by several

     minutes of arc.

     Information about the  program  may  be  obtained  from  its



     /usr/lib/startab, /usr/lib/moontab


     azel (VI)

     American Ephemeris and Nautical Almanac, for the appropriate

     years;  also,  the  Explanatory  Supplement  to the American

     Ephemeris and Nautical Almanac.


     R. Morris