Server time and php time


can you explain why php time and server time are different

$today = date("F j, Y, g:i a");
echo $today;
echo "<br>".shell_exec("date");

November 18, 2010, 12:56 am => time returned by php date
Thu Nov 18 02:56:31 AST 2010 => server time

There are 2 hours difference , why ?
Thank you

Is the server in the same timezone as where you are located?

infact it was the problem, I fixed it using date.timezone in my php.ini (same timezone such as my server timezone), thank you.