Great additions Aldebaran!

DateTime can do date arithmetic as simply as:

my $dt = DateTime->new(
    year      => 2021,
    month     => 4,
    day       => 5,
    hour      => 2,
    time_zone => 'Africa/Nairobi',
);
# or, create a DateTime object from an ISO timestring
my $isostr = '2021-10-11T11:13:57';
my $dt = DateTime::Format::ISO8601->parse_datetime($isostr);
# add a second to what $dt currently holds
$dt->add(seconds => 1);
[download]

Regarding your other questions, I have no clue about celestial mechanics. Nonetheless I have whipped up a Perl sub to get you the elevation given coordinates. It uses a site which I am not sure if they would like people using their services in this way. So with that in mind:

# usage:
# my $elevation = get_elevation_from_coordinates(15.6325, 38.245833, 0
+);
sub get_elevation_from_coordinates {
    my ($lat, $lon, $debug) = @_;

    $debug //= 0;

    my $ua = LWP::UserAgent->new(
        agent => 'Mozilla/5.0 (X11; Linux x86_64; rv:78.0) Gecko/20100
+101 Firefox/78.0',
    );

    my $response;
    my $payload =
        'latitude='.$lat
        .'&longitude='.$lon
        .'&application_max_assets_mtime=1559625591'
    ;
    my $payloadlen = length($payload);
        # this request was translated from Curl command-line
        # by [Corion]'s https://corion.net/curl2lwp.psgi
    my $req = HTTP::Request->new(
        'POST' => 'https://www.mapcoordinates.net/admin/component/edit
+/Vpc_MapCoordinates_Advanced_GoogleMapCoords_Component/Component/json
+-get-elevation',
    [
        'Connection'      => 'keep-alive',
        'Accept'          => '*/*',
        'Accept-Encoding' => 'gzip, x-gzip, deflate, x-bzip2, bzip2',
        'Accept-Language' => 'en-US,en;q=0.5',
#        'Host'            => 'www.mapcoordinates.net:443',
        'Referer'         => 'https://www.mapcoordinates.net/en',
        'User-Agent'     => 'Mozilla/5.0 (X11; Linux x86_64; rv:78.0) 
+Gecko/20100101 Firefox/78.0',
        'Content-Length' => $payloadlen,
        'Content-Type'   => 'application/x-www-form-urlencoded; charse
+t=UTF-8',
        'DNT'            => '1',
        'Origin'         => 'https://www.mapcoordinates.net',
        'X-Requested-With' => 'XMLHttpRequest'
    ],
        $payload
    );
    die "call to HTTP::Request has failed" unless $req;

    if( $debug > 0 ){ print "$0 : $payload\n$0 : sending above payload
+, of $payloadlen bytes...\n" }

    $response = $ua->request($req);
    die "Error fetching: ".$response->status_line
        unless $response->is_success;

    my $content = $response->decoded_content;
    my $data = Data::Roundtrip::json2perl($content);
    die "failed to parse received data:\n$content\n"
     unless exists $data->{'elevation'};

    return $data->{'elevation'};
}
[download]

bw, bliako

Geo::WebService::Elevation::USGS - Elevation queries against USGS web services.

Thanks for this. It works for trump's (real) tower but scylla is shown to be somewhere near Hades (for a country with planetal ambitions, their map services are curiously modest to confine within the national boundaries and that "feet" default indicates possible time-warp to past eras):

use  Geo::WebService::Elevation::USGS;
use Data::Dumper;
my $eq =  Geo::WebService::Elevation::USGS->new(
    timeout => 60,
);
# white house
my $x = $eq->elevation(38.91205168958467, -77.03355236501928);
print Dumper($x);

# scilla sicily
$x = $eq->elevation(38.17378844699463, 15.83642789839883);
print Dumper($x);
[download]

$VAR1 = {
          'Units' => 'Feet',
          'Data_Source' => '3DEP 1/3 arc-second',
          'y' => '38.9120516895847',
          'Elevation' => '96.95',
          'x' => '-77.0335523650193'
        };
$VAR1 = {
          'y' => '38.1737884469946',
          'x' => '15.8364278983988',
          'Elevation' => '-1000000',
          'Units' => 'Feet',
          'Data_Source' => '3DEP 1/3 arc-second'
        };
[download]

Thanks for this. It works for trump's (real) tower but scylla is shown to be somewhere near Hades (for a country with planetal ambitions, their map services are curiously modest to confine within the national boundaries and that "feet" default indicates possible time-warp to past eras):

Trump has been relegated to a third-world nation (Florida), and with the guvmint, it seems to depend on who and how you ask:

fritz@hogan-Lenovo-IdeaPad-S145-15IWL:~/Documents$ ./7.mp.pl 
Subroutine get_logger redefined at ./7.mp.pl line 41.
INFO: ./7.mp.pl
in new scylla on 2022-02-18T03:22:31 (1645150951 seconds unix-epoch) t
+imezone: Europe/Rome (lat: 38.1737884469946, lon: 15.8364278983988)
Moon age: 16.1131124830837 days
Moon phase: 54.6 % of cycle (birth-to-death)
Moon's illuminated fraction: 98.0 % of full disc
important moon phases around the event:
  New Moon      = Mon Jan 31 22:49:10 2022
  First quarter = Tue Feb  8 06:51:53 2022
  Full moon     = Wed Feb 16 09:59:41 2022
  Last quarter  = Wed Feb 23 15:34:32 2022
  New Moon      = Wed Mar  2 10:38:16 2022
end event.

INFO: return from the google is 1291 meters
INFO: in new scylla on 2022-02-18T03:22:31 (1645150951 seconds unix-ep
+och) timezone: Europe/Rome (lat: 38.1737884469946, lon: 15.8364278983
+988) at height 1293  meters
INFO: Object    Azimuth        Elevation
INFO: Venus    103.996877720637        -9.60439269992599
INFO: Jupiter    57.162019344654        -45.6099678242824
INFO: Moon    232.083188637894        50.0250955497636
INFO: Saturn    84.3881395776426        -34.0613320748201
fritz@hogan-Lenovo-IdeaPad-S145-15IWL:~/Documents$ cat 7.mp.pl 
#!/usr/bin/perl 

use v5.030;    # strictness implied
use warnings;
use feature qw[ signatures ];
no warnings qw[ experimental::signatures ];

use Astro::Coord::ECI::Utils 'deg2rad';
use Astro::Coords;
use Astro::MoonPhase;
use Astro::Telescope;
use Data::Dumper;
use DateTime;
use DateTime::Format::ISO8601;
use DateTime::TimeZone;
use Log::Log4perl;
use Try::Tiny;

our $debug = 0;
my $time_str = "03:22:31";
my $alt      = 0;
my $date_str = "2022-02-18";

my @events = (


  {
    "name"     => "in new scylla",
    "date"     => $date_str,
    "time"     => $time_str,
    "location" => { lon => 15.83642789839883, lat => 38.17378844699463
+ },
  },

);

# Not wanting to divine the configuration file for Log::Log4perl, modu
+le used in
# the query. Better for SSCCE considerations. thx parv
{

  package Log::Log4perl;
  sub get_logger ($pkg) { return bless [], $pkg; }

  sub show  (@arg)             { warn @arg, "\n"; }
  sub debug ( $ignore, @rest ) { show( 'DEBUG: ',   @rest ); }
  sub info  ( $ignore, @rest ) { show( 'INFO: ',    @rest ); }
  sub warn  ( $ignore, @rest ) { show( 'WARNING: ', @rest ); }

  sub error ( $ignore, @rest ) { die 'ERROR: ', @rest, "\n"; }
}

my $logger = Log::Log4perl->get_logger();
$logger->info("$0");

## event loop

for my $event (@events) {
  my $epoch = parse_event($event);
      print event2str($event) . "\n";

    my (    $MoonPhase,
        $MoonIllum,
        $MoonAge,
        $MoonDist,
        $MoonAng,
        $SunDist,
        $SunAng
    ) = phase($epoch);
    print "Moon age: $MoonAge days\n";
    print "Moon phase: ".sprintf("%.1f", 100.0*$MoonPhase)." % of cycl
+e (birth-to-death)\n";
    print "Moon's illuminated fraction: ",sprintf("%.1f", 100.0*$MoonI
+llum)." % of full disc\n";

    print "important moon phases around the event:\n";
    my @phases = phasehunt($epoch);
    print "  New Moon      = ", scalar(localtime($phases[0])), "\n";
    print "  First quarter = ", scalar(localtime($phases[1])), "\n";
    print "  Full moon     = ", scalar(localtime($phases[2])), "\n";
    print "  Last quarter  = ", scalar(localtime($phases[3])), "\n";
    print "  New Moon      = ", scalar(localtime($phases[4])), "\n";
    print "end event.\n\n";

## determine altitude
  # usage:
  die unless exists $event->{location};    # restriction
  my $return = get_elevation_from_coordinates( $event->{location}->{la
+t},
    $event->{location}->{lon}, $debug );
  $logger->info("return from the google is $return meters");
  my $observer = $return + 2;              #(most people stand)
  $logger->info( event2str($event) . " at height $observer  meters" );
  $logger->info("Object\tAzimuth\t\tElevation");
  for my $name (qw/Venus Jupiter Moon Saturn/) {

    my $planet = Astro::Coords->new( planet => $name );

    # use DateTime
    my $date = DateTime->from_epoch( epoch => $epoch, time_zone => 'UT
+C' );
    $planet->datetime($date);

    $planet->telescope(
      Astro::Telescope->new(
        Name => $event->{name},
        Long => deg2rad( $event->{location}->{lon} ),
        Lat  => deg2rad( $event->{location}->{lat} ),
        Alt  => $observer,                              #meters above 
+sea level
      )
    );

    my $az = $planet->az( format => 'deg' );
    my $el = $planet->el( format => 'deg' );
    $logger->info("$name\t$az\t\t$el");

  }
  ## end planets loop
}
## end event loop

sub event2str {
  my $event = shift;

  if ( !exists $event->{_is_parsed} ) {
    warn "event has not been parsed, just dumping it...";
    print Dump($event);
  }
  my $str =
      $event->{name} . " on "
    . $event->{datetime} . " ("
    . $event->{datetime}->epoch
    . " seconds unix-epoch)"
    . " timezone: "
    . $event->{datetime}->time_zone->name;
  if ( exists $event->{location} ) {
    if ( ref( $event->{location} ) eq 'HASH' ) {
      $str .=
          " (lat: "
        . $event->{location}->{lat}
        . ", lon: "
        . $event->{location}->{lon} . ")";
    }
    else { $str .= "(" . $event->{location} . ")" }
  }
  return $str;
}

sub parse_event {
  my $event = shift;

  $debug //= 0;
  if ( !exists $event->{date} ) { die "date field is missing from even
+t." }

  my $datestr = $event->{date};

  die "event does not have a 'name' field, please specify one, anythin
+g really."
    unless exists $event->{name};

  my $timestr = "00:00:01";
  if ( exists $event->{time} ) {
    $timestr = $event->{time};
    print "event2epoch(): setting time to '$timestr' ...\n"
      if $debug > 0;
    die "time '$timestr' is not valid, it must be in the form 'hh:mm:s
+s'."
      unless $timestr =~ /^\d{2}:\d{2}:\d{2}$/;
  }
  else { $event->{time} = $timestr }

  my $isostr = $datestr . 'T' . $timestr;
  my $dt     = DateTime::Format::ISO8601->parse_datetime($isostr);
  die "failed to parse date '$isostr', check date and time fields."
    unless defined $dt;
  $event->{datetime} = $dt;

  my $tzstr = 'UTC';
  if ( exists $event->{timezone} ) {
    $tzstr = $event->{timezone};
    print
"event2epoch(): found a timezone via 'timezone' field as '$tzstr' (tha
+t does not mean it is valid) ...\n"
      if $debug > 0;
  }
  elsif ( exists $event->{location} ) {
    my $loc = $event->{location};
    if ( ( ref($loc) eq '' ) && ( $loc =~ /^[a-zA-Z]$/ ) ) {

      # we have a location string
      my @alltzs = DateTime::TimeZone->all_names;
      my $tzstr;
      for (@alltzs) {
        if ( $_ =~ /$loc/i ) { $tzstr = $_; last }
      }
      die
"event's location can not be converted to a timezone, consider specify
+ing the 'timezone' directly or setting 'location' coordinates with: \
+[lat,lon\]."
        unless $tzstr;
      print
"event2epoch(): setting timezone via 'location' name to '$timestr' ...
+\n"
        if $debug > 0;
    }
    elsif ( ( ref($loc) eq 'HASH' )
      && ( exists $loc->{lat} )
      && ( exists $loc->{lon} ) )
    {
      # we have a [lat,lon] array for location
      require Geo::Location::TimeZone;
      my $gltzobj = Geo::Location::TimeZone->new();
      $tzstr = $gltzobj->lookup( lat => $loc->{lat}, lon => $loc->{lon
+} );
      if ( !$tzstr ) {
        die "timezone lookup from location coordinates lat:"
          . $loc->{lat}
          . ", lon:"
          . $loc->{lon}
          . " has failed.";
      }
      print "event2epoch(): setting timezone via 'location' coordinate
+s lat:"
        . $loc->{lat}
        . ", lon:"
        . $loc->{lon}
        . " ...\n"
        if $debug > 0;
    }
  }
  if ($tzstr) {
    print "event2epoch(): deduced timezone to '$tzstr' and setting it 
+...\n"
      if $debug > 0;
    try {
      $dt->set_time_zone($tzstr)
    }
    catch {
      die "$_\n failed to set the timezone '$tzstr', is it valid?"
    }
  }

  $event->{_is_parsed} = 1;
  $event->{epoch}      = $dt->epoch;
  return $event->{epoch};
}

sub get_elevation_from_coordinates {
  my ( $lat, $lon, $debug ) = @_;

  use LWP::UserAgent;
  use HTTP::Request;
  use Data::Roundtrip;

  $debug //= 0;

  my $ua = LWP::UserAgent->new( agent =>
      'Mozilla/5.0 (X11; Linux x86_64; rv:78.0) Gecko/20100101 Firefox
+/78.0', );

  my $response;
  my $payload =
      'latitude='
    . $lat
    . '&longitude='
    . $lon
    . '&application_max_assets_mtime=1559625591';
  my $payloadlen = length($payload);

  # this request was translated from Curl command-line
  # by [Corion]'s https://corion.net/curl2lwp.psgi
  my $req = HTTP::Request->new(
    'POST' =>
'https://www.mapcoordinates.net/admin/component/edit/Vpc_MapCoordinate
+s_Advanced_GoogleMapCoords_Component/Component/json-get-elevation',
    [
      'Connection'      => 'keep-alive',
      'Accept'          => '*/*',
      'Accept-Encoding' => 'gzip, x-gzip, deflate, x-bzip2, bzip2',
      'Accept-Language' => 'en-US,en;q=0.5',

      #        'Host'            => 'www.mapcoordinates.net:443',
      'Referer'    => 'https://www.mapcoordinates.net/en',
      'User-Agent' =>
        'Mozilla/5.0 (X11; Linux x86_64; rv:78.0) Gecko/20100101 Firef
+ox/78.0',
      'Content-Length'   => $payloadlen,
      'Content-Type'     => 'application/x-www-form-urlencoded; charse
+t=UTF-8',
      'DNT'              => '1',
      'Origin'           => 'https://www.mapcoordinates.net',
      'X-Requested-With' => 'XMLHttpRequest'
    ],
    $payload
  );
  die "call to HTTP::Request has failed" unless $req;

  if ( $debug > 0 ) {

    $logger->debug(
      "$0 : $payload\n$0 : sending above payload, of $payloadlen bytes
+...");
  }

  $response = $ua->request($req);
  die "Error fetching: " . $response->status_line
    unless $response->is_success;

  my $content = $response->decoded_content;
  my $data    = Data::Roundtrip::json2perl($content);
  die "failed to parse received data:\n$content\n"
    unless exists $data->{'elevation'};

  return $data->{'elevation'};
}

__END__

fritz@hogan-Lenovo-IdeaPad-S145-15IWL:~/Documents$
[download]

My units are meters here from what we did before, but Americans won't understand what doesn't comport with their religion: football.