The |date_822 filter formats a date type tag (#DATE, #DATE_REDAC, etc.) according to the RFC 822 standard (used for the <pubdate> in some RSS 2.0 feeds — notably on photocast).
Example:
the date 2008-10-03 08:22:00 will be displayed as Fri, 03 Oct 2008 08:22:00 +0200