Yes, sin and cos are the functions you need.

#!/usr/bin/perl
use warnings;
use strict;

use Tk;

use constant PI => 4 * atan2(1, 1);

my ($center_x, $center_y) = (25, 25);
my $radius = 20;
my $object_count = 19;

my $mw = 'MainWindow'->new(-title  => 'Objects in circle');
$mw->Label(-text => 'Center')->grid(-row    => $center_x,
                                    -column => $center_y,
                                   );
my @objects = map "Object $_", 1 .. $object_count;
my $step = 2 * PI / (1 + $#objects);
for my $i (0 .. $#objects) {
    my $angle = $i * $step;
    my $x = $center_x + $radius * cos $angle;
    my $y = $center_y + $radius * sin $angle;
    $mw->Label(-text => $objects[$i])->grid(-row    => $y,
                                            -column => $x,
                                           );
}

MainLoop();
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