Astro::Time(3pm)

NAME
Astro::Time - Time based astronomical routines

SYNOPSIS
    use Astro::Time;

    $dayno = cal2dayno($day, $month, $year);
    print "It's a leap year!\n" if (leap($year));
    $lmst = mjd2lst($mjd, $longitude, $dUT1);
    $turns = str2turn($string, 'H');
    $str = turn2str($turn, 'D', $sig);

DESCRIPTION
Astro::Time contains an assorted set Perl routines for time based conversions, such as conversion between calendar dates and Modified Julian day and conversion of UT to local sidereal time. Include are routines for conversion between numerical and string representation of angles.

AUTHOR
Chris Phillips Chris.Phillips@csiro.au

FUNCTIONS

turn2str
      $str = turn2str($turn, $mode, $sig);
      $str = turn2str($turn, $mode, $sig, $strsep);

     Convert fraction of a turn into string representation
       $turn   Angle in turns
       $mode   Mode of string to convert to:
                'H' for hours
                'D' for degrees
       $sig    number of significant figures
       $strsep String separator (override for default $Astro::Time::StrSep)
    Note:
     The behavior can be modified by the following two variables:
      $Astro::Time::StrZero   Minimum number of leading digits (zero padded
                              if needed)
      $Astro::Time::StrSep    (Overridden by optional fourth argument)
        Deliminator used in string (Default ':')
        This may also equal one of a number of special values:
          'HMS'           12H45M12.3S or 170D34M56.2S
          'hms'           12h45m12.3s or 170d34m56.2s
          'deg'           170d34'56.2"

deg2str
      $str=deg2str($deg, $mode, $sig);

     Convert degrees into string representation
       $deg   angle in degrees
       $mode  mode of string to convert to:
               'H' for hours
               'D' for degrees
       $sig   number of significant figures
     See note for turn2str

rad2str
      $str=rad2str($rad, $mode, $sig);

     Convert radians into string representation
       $rad    angle in radians
       $mode   mode of string to convert to:
                'H' for hours
                'D' for degrees
       $sig is number of significant figures
     See note for turn2str

str2turn
      $turns = str2turn($string,$mode);

     Convert angle from string representation into fraction of a turn
       $string    a : or space delimited angle
       $mode      type of angle
                   'H' if $string is in hours,min,sec
                   'D' if $string is in deg,arcmin,arcsec
     The format of $string can be fairly flexible e.g.:
        12.2
        12:34
        12:34:45.1
       -23 34 12.3
       -34 34.3

     Note: You cannot mix spaces and :

str2deg
      $degrees=str2deg($string,$mode);

     Convert angle from string representation into degrees
       $string   a : or space delimited angle
       $mode     'H' if $string is in hours,min,sec
                 'D' if $string is in deg,arcmin,arcsec
     See note for str2turn

str2rad
      $radians=str2rad($string,$mode);

     Convert angle from string representation into radians
       $string   a : or space delimited angle
       $mode     'H' if $string is in hours,min,sec
                 'D' if $string is in deg,arcmin,arcsec
     See note for str2turn

hms2time
      ($time) = hms2time($hour, $minute, $second);
      ($time) = hms2time($hour, $minute, $second, $mode);

     Returns the day fraction given hours minutes and seconds (or degrees)
       $time        Day fraction
       $hour        Hours
       $minutes     Minutes
       $second      Seconds
       $mode        'H' or 'D' to interpret as hours or degrees (default
                    hours)

time2hms
      ($sign, $hour, $minute, $second) = time2hms($time, $mode, $sig);

     Returns hours (or degrees), minutes and seconds given the day fraction
       $sign      Sign of angle ('+' or '-')
       $hour      Hours
       $minutes   Minutes
       $second    Seconds
       $time      Day fraction
       $mode      Return degrees or Hours?
                   'H' for hours
                   'D' for degrees
       $sig       Number of significant digits for $second

deg2rad
      $rad=deg2rad($deg);
     Convert degrees to radians

rad2deg
      $deg=rad2deg($rad);
     Convert radians to degrees

turn2rad
      $rad=turn2rad($turn);
     Convert turns to radians

rad2turn
      $turn=rad2turn($rad);
     Convert radians to turns

turn2deg
      $deg=turn2deg($turn);
     Convert turns to radians

deg2turn
      $turn=deg2turn($deg);
     Convert degrees to turns

cal2dayno
      $dayno = cal2dayno($day, $month, $year);

     Returns the day number corresponding to $day of $month in $year.

dayno2cal
      ($day, $month) = dayno2cal($dayno, $year);

     Return the $day and $month corresponding to $dayno of $year.

leap
      $isleapyear = leap($year);

     Returns true if $year is a leap year.
       $year    year in full

yesterday
      ($dayno, $year) = yesterday($dayno, $year);
      ($day, $month, $year) = yesterday($day, $month, $year);

     Winds back the day number by one, taking account of year wraps.
       $dayno       Day number of year
       $year        Year
       $month       Month
       $day         Day of month

tomorrow
      ($dayno, $year) = tomorrow($dayno, $year);
      ($day, $month, $year) = tomorrow($day, $month, $year);

     Advances the day number by one, taking account of year wraps.
       $dayno       Day number of year
       $year        Year
       $month       Month
       $day         Day of month

mjd2cal
      ($day, $month, $year, $ut) = mjd2cal($mjd);

     Converts a modified Julian day number into calendar date (universal
     time). (based on the slalib routine sla_djcl).
        $mjd     Modified Julian day (JD-2400000.5)
        $day     Day of the month.
        $month   Month of the year.
        $year    Year
        $ut      UT day fraction

cal2mjd
      $mjd = cal2mjd($day, $month, $year, $ut);

     Converts a calendar date (universal time) into modified Julian day
     number.
        $day     Day of the month.
        $month   Month of the year.
        $year    Year
        $ut      UT dayfraction
        $mjd     Modified Julian day (JD-2400000.5)

mjd2dayno
      ($dayno, $year, $ut) = mjd2dayno($mjd);

     Converts a modified Julian day number into year and dayno (universal
     time).
        $mjd     Modified Julian day (JD-2400000.5)
        $year    Year
        $dayno   Dayno of year

dayno2mjd
      $mjd = dayno2mjd($dayno, $year, $ut);

     Converts a dayno and year to modified Julian day
        $mjd     Modified Julian day (JD-2400000.5)
        $year    Year
        $dayno   Dayno of year

now2mjd
      $mjd = now2mjd()

jd2mjd
      $mjd = jd2mjd($jd);

     Converts a Julian day to Modified Julian day
        $jd      Julian day
        $mjd     Modified Julian day

mjd2jd
      $jd = mjd2jd($mjd);

     Converts a Modified Julian day to Julian day
        $mjd     Modified Julian day
        $jd      Julian day

mjd2time
      $str = mjd2time($mjd);
      $str = mjd2time($mjd, $np);

     Converts a Modified Julian day to a formatted string
        $mjd     Modified Julian day
        $str     Formatted time
        $np      Number of significant digits for fraction of a sec. Default 0

mjd2vextime
      $str = mjd2vextime($mjd);
      $str = mjd2vextime($mjd, $np);

     Converts a Modified Julian day to a vex formatted string
        $mjd     Modified Julian day
        $str     Formatted time
        $np      Number of significant digits for fraction of a sec. Default 0

mjd2epoch
      $time = mjd2epoch($mjd);

     Converts a Modified Julian day to unix Epoch (seconds sinve 1 Jan 1970)
     Rounded to the nearest second
        $mjd     Modified Julian day
        $tie     Seconds since 1 Jan 1970

gst
      $gst  = gst($mjd);
      $gmst = gst($mjd, $dUT1);
      $gtst = gst($mjd, $dUT1, $eqenx);

     Converts a modified Julian day number to Greenwich sidereal time
       $mjd     modified Julian day (JD-2400000.5)
       $dUT1    difference between UTC and UT1 (UT1 = UTC + dUT1) (seconds)
       $eqenx   Equation of the equinoxes (not yet supported)
       $gst     Greenwich sidereal time (turns)
       $gmst    Greenwich mean sidereal time (turns)
       $gtst    Greenwich true sidereal time (turns)

mjd2lst
      $lst = mjd2lst($mjd, $longitude);
      $lmst = mjd2lst($mjd, $longitude, $dUT1);
      $ltst = mjd2lst($mjd, $longitude, $dUT1, $eqenx);

     Converts a modified Julian day number into local sidereal time (lst),
     local mean sidereal time (lmst) or local true sidereal time (ltst).
     Unless high precisions is required dUT1 can be omitted (it will always
     be in the range -0.5 to 0.5 seconds).
       $mjd         Modified Julian day (JD-2400000.5)
       $longitude   Longitude for which the LST is required (turns)
       $dUT1        Difference between UTC and UT1 (UT1 = UTC + dUT1)(seconds)
       $eqenx       Equation of the equinoxes (not yet supported)
       $lst         Local sidereal time (turns)
       $lmst        Local mean sidereal time (turns)
       $ltst        Local true sidereal time (turns)

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

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

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.

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)
        $dUT1      - Difference between UTC and UT1 (UT1 = UTC + dUT1)
                                                                    (seconds)
        $mjd         The modified Julian day corresponding to $lmst on $dayno

month2str
      $monthstr = month2str($month);
      $longmonthstr = month2str($month,1);

      This routine returns the name of the given month (as a number 1..12),
      where 1 is January. The default is a 3 character version of the month
      ('Jan', 'Feb', etc) in the second form the full month is returned

      The required inputs are :
        $month      - The month in question with 1 == January.

mjd2weekday
      $weekday = mjd2weekday($mjd);

     Returns the weekday correspondig to the given MJD.
     0 ==> Monday. May not work for historical dates.

        $mjd     Modified Julian day (JD-2400000.5)

mjd2weekdaystr
      $weekdaystr = mjd2weekdaystr($mjd);

     Returns the name of the weekday correspondig to the given MJD.
     May not work for historical dates.

        $mjd     Modified Julian day (JD-2400000.5)

str2month
      $month = month2str($monthstr);

      Given the name of a month (in English), this routine returns the
      an integer between 1 and 12, where 1 is January. Full month names of
      3 character abbreviations are acceptable. Minumum matching (e.g. "Marc")
      is not supported.

      The required inputs are :
        $month      - Name of the month ('Jan', 'January', 'Feb', 'February' etc)