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  while ($lst>1.0) {
    $lst-= 1;
  }
  while ($lst < 0.0) {
    $lst += 1;
  }
  return $lst;
}

=item B<cal2lst>

  $lst = cal2lst($day, $month, $year, $ut, $longitude);
  $lmst = cal2lst($day, $month, $year, $ut, $longitude, $dUT1);
  $ltst = cal2lst($day, $month, $year, $ut, $longitude, $dUT1, $eqenx);

 Wrapper to mjd2lst using calendar date rather than mjd

=cut

sub cal2lst($$$$$;$$) {
  my ($day, $month, $year, $ut, $longitude, $dUT1, $eqenx) = @_;
  my $mjd = cal2mjd($day, $month, $year, $ut);
  return undef if (!defined $mjd);

  return mjd2lst($mjd, $longitude, $dUT1, $eqenx);
}

=item B<dayno2lst>

  $lst = dayno2lst($dayno, $year, $ut, $longitude);
  $lmst = dayno2lst($dayno, $year, $ut, $longitude, $dUT1);
  $ltst = dayno2lst($dayno, $year, $ut, $longitude, $dUT1, $eqenx);

 Wrapper to mjd2lst using calendar date rather than mjd

=cut

sub dayno2lst($$$$;$$) {
  my ($dayno, $year, $ut, $longitude, $dUT1, $eqenx) = @_;
  my $mjd = dayno2mjd($dayno, $year, $ut);
  return undef if (!defined $mjd);

  return mjd2lst($mjd, $longitude,  $dUT1, $eqenx);
}

# Not verified

=item B<rise>

  ($lst_rise, $lst_set) = rise($ra, $dec, $obslat, $el_limit);

 Return the lst rise and set time of the given source
   $lst_rise, $lst_set  Rise and set time (turns)
   $ra, $dec            RA and Dec of source (turns)
   $obslat              Latitude of observatory (turns)
   $el_limit            Elevation limit of observatory
                                          (turns, 0 horizontal)
 Returns 'Circumpolar'  if source circumpolar
 Returns  undef         if source never rises

 Uses the formula:
   cos $z_limit = sin $obslat * sin $dec + cos $obslat * cos $dec 
                  * cos $HA
   where:
    $z_limit is the zenith angle limit corresponding to $el_limit
    $HA is the Hour Angle of the source
NOTE: For maximum accuracy source coordinated should be precessed to
      the current date.

=cut

sub rise ($$$$) {
  #print "rise: Got @_\n";
  my ($ra, $dec, $obslat, $el_limit) = @_;
  $ra = turn2rad($ra);
  $dec = turn2rad($dec);
  $obslat = turn2rad($obslat);
  $el_limit = turn2rad($el_limit);

  my $z_limit = $PI/2-$el_limit;

  #print "Check it\n";

  # Check whether the source ever rises or is circumpolar
  my $z = acos(sin($obslat)*sin($dec) + cos($obslat)*cos($dec)); # Highest point
  return (undef) if ($z>$z_limit);

  #print "Got here\n";

  $z = acos(sin($obslat)*sin($dec) - cos($obslat)*cos($dec)); # Lowest point

  return ('Circumpolar') if ($z<$z_limit);

  my $cos_ha = (cos($z_limit) - sin($obslat)*sin($dec))
    /(cos($obslat)*cos($dec));
  my $ha = acos($cos_ha);

  my $lst_rise =  $ra - $ha;
  my $lst_set = $ra + $ha;

  $lst_rise += 2*$PI if ($lst_rise < 0.0);
  $lst_set -= 2*$PI if ($lst_set >= 2*$PI);

  return rad2turn($lst_rise), rad2turn($lst_set);
}

=item B<lst2mjd>

  $mjd = lst2mjd($lmst, $dayno, $year, $longitude);
  $mjd = lst2mjd($lmst, $dayno, $year, $longitude, $dUT1);

  This routine calculates the modified Julian day number corresponding
  to the local mean sidereal time $lmst at $longitude, on a given UT
  day number ($dayno).  Unless high precision is required dUT1 can be
  omitted.

  The required inputs are :
    $lmst      - The local mean sidereal time (turns)
    $dayno     - The UT day of year for which to do the conversion
    $year      - The year for which to do the conversion
    $longitude - The longitude of the observatory (turns)