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Been a while since I have posted as OP with the Perlpocalypse and all. I took a tour "out there" to see what else was going on. I worked a bit with python, but, as a guy who started comp sci in the punchcard era, I can't look at fixed form source and call it "progress." (Do they have pythontidy like we have perltidy?)

I also took a gander at Usenet. It was nice to see some old names, but it has the same cooties of spammers and pornographers that mutate faster than one's killfile. comp.unix.programmer was still viable, as well as comp.lang.fortran, but I couldn't figure out the proprietary client the provider wanted me to use, so that fizzled out. (That's a nice way of saying I got locked out of my own account with failed attempts.)

I've had several scripts that I've been fiddling with in the meantime. This one came up in the context of Moon phase on historical events. I present attempts to iterate over the closed interval of a lunar cycle within the methodology of DateTime. It's not complete, but I've got output I don't understand, so I want to put it up for review. Let me just get source out there first:

#!/usr/bin/perl 

use v5.030;
use warnings;

use Astro::Coords;
use Astro::MoonPhase;
use DateTime;
use DateTime::Format::ISO8601;
use Log::Log4perl;

my $file = '/home/hogan/Documents/hogan/logs/3.log4perl.txt';

unlink $file or warn "Could not unlink $file: $!";
my $log_conf4 = "/home/hogan/Documents/hogan/logs/conf_files/3.conf";
Log::Log4perl::init($log_conf4);    #info
my $logger = Log::Log4perl->get_logger();
## time program
my $now   = DateTime->now( time_zone => 'UTC' );
$logger->info("$0 executed at $now");
# or, create a DateTime object from an ISO timestring
my $isostr = '2021-10-09T11:13:57';    # jd 2459496.96802
my $dt     = DateTime::Format::ISO8601->parse_datetime($isostr);

my @phases = phasehunt($dt);
$logger->info("@phases");
my $start_epoch = $phases[0];
my $end_epoch   = $phases[4];
my $diff        = $end_epoch - $start_epoch;

my $hard_bottom = int($start_epoch);
$logger->info("integer bottom is $hard_bottom");
$logger->info( "lunation is " . $diff / ( 24 * 60 * 60 ) . " days" );
$logger->info( "degrees covered per day is "
    . 360 / ( $diff / ( 24 * 60 * 60 ) )
    . " degrees" );
## end prelims for moonphase
## prelims for planets

my $traveler1 = Astro::Coords->new( planet => 'Moon' ); 
my $traveler2 = Astro::Coords->new( planet => 'Venus' );
my $traveler3 = Astro::Coords->new( planet => 'Jupiter' );

my $moon_ra  = 4.15;    # values make initial while condition true
my $venus_ra = 4.2;     # values make initial while condition true
my $jup_ra = 7;     # values make initial while condition true

while ( $moon_ra < $venus_ra ) {
  ## moon
  $traveler1->datetime($dt);
  $moon_ra = $traveler1->ra( format => q/deg/ );
  ## venus
  $traveler2->datetime($dt);
  $venus_ra = $traveler2->ra( format => q/deg/ );

  my $random = rand();
  if ( $random > .99 ) {
    $logger->info("dt is $dt");
    $logger->info("Moon ra is $moon_ra");
    $logger->info("venus ra is $venus_ra");
  }

  ## add a second to what $dt currently holds
  $dt->add( seconds => 1 );
}

my $et        = $dt->clone->subtract( seconds => 1 );
my $et_julian = $et->jd;
$logger->info("dt is $dt");
$logger->info("et is $et");
$logger->info("Moon ra is $moon_ra");
$logger->info("venus ra is $venus_ra");
$logger->info("Julian equality is $et_julian");


my $later = DateTime->now( time_zone => 'UTC' );
 
my $seconds_dur = $later->subtract_datetime_absolute($now);
$logger->info("Program duration is $seconds_dur seconds");
__END__
[download]

Typical abridged output:

2021/10/12 17:44:15 INFO ./2.vj.pl executed at 2021-10-12T23:44:15 
2021/10/12 17:44:15 INFO -1952337.6024127 -1378241.1266014 -714314.659
+416676 -4036.13566160202 592540.73432833 
2021/10/12 17:44:15 INFO integer bottom is -1952337 
2021/10/12 17:44:15 INFO lunation is 29.4546103789471 days 
2021/10/12 17:44:15 INFO degrees covered per day is 12.222195281772 de
+grees 
2021/10/12 17:44:15 INFO dt is 2021-10-09T11:20:59 
2021/10/12 17:44:15 INFO Moon ra is 235.845969901601 
2021/10/12 17:44:15 INFO venus ra is 239.201830385495 
2021/10/12 17:44:16 INFO dt is 2021-10-09T11:23:42 
2021/10/12 17:44:16 INFO Moon ra is 235.865530833331 
2021/10/12 17:44:16 INFO venus ra is 239.203970696164 
...
2021/10/12 17:45:02 INFO venus ra is 239.628594527327 
2021/10/12 17:45:02 INFO dt is 2021-10-09T20:25:16 
2021/10/12 17:45:02 INFO Moon ra is 239.625074172142 
2021/10/12 17:45:02 INFO venus ra is 239.629628154514 
2021/10/12 17:45:02 INFO dt is 2021-10-09T20:25:47 
2021/10/12 17:45:02 INFO et is 2021-10-09T20:25:46 
2021/10/12 17:45:02 INFO Moon ra is 239.630096069291 
2021/10/12 17:45:02 INFO venus ra is 239.630025731277 
2021/10/12 17:45:02 INFO Julian equality is 2459497.35122685 
2021/10/12 17:45:02 INFO Program duration is DateTime::Duration=HASH(0
+x5642bb935d40) seconds
[download]

$et is to be the second at which the moon and venus conjoin, ie, have the same right ascension. The problem is that I check the data with John Walker's Fourmilab ephemeris and use the option for univeral time. The time defined in perl thus:

my $isostr = '2021-10-09T11:13:57';

is inputed without the T, and with the radio button activated, thus:

2021-10-09 11:13:57

But that's not our value to check, which should be $et, namely:

2021-10-09 20:25:46

It would seem that the moon is well past Venus by the margin of almost 2 hours. I tried to spitball if it might be using a different idea of coincidence with non-point masses. The full moon is about a half a degree. It's certainly not half full, and the dark edge hits venus first. In the prelims, I calculated that angle the moon moves through in a day to be 12.2 degrees. A quarter of a degree takes the moon about a half hour. Our answer seems to be at least 3 times out of this range as fourmilab has the conjunction between this interval, I:

2021-10-09 18:30:00

And this time:

2021-10-09 18:40:00

Q1) Do these bodies conjoin at $et or in the interval I? How does perl represent the moon in Astro::Coords? (For example, is the right ascension that of the center?}

I didn't expect $phases[0] to be negative. Given that it was defined by

my @phases = phasehunt($dt);

Q2) How do I take $dt and $phases[0] and get epoch time?

Q3) How do I get the duration of the program run to display correctly? I thought I followed Dave Rolsky's example.

I wanted to be able to calculate the duration of the transit of the moon from venus to jupiter before it happened.

Thanks for comments,

In reply to iterating over time with DateTime to obtain values with Astro::Coords by Aldebaran

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