Code:
/usr/bin/php -q /home/luke83/public_html/cron/cron_job.php >>/home/luke83/public_html/cron/cron_log.txt 2>&1
Is the format that I use and it works on Chopin.
Any output from cron_job.php or any error messages are logged into cron_log.txt, that way you can
1) see if the cron job is running
2) see any errors