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