I think you can get iCal to subscribe to a WebDAV calendar for moon phases here:

http://icalshare.com/calendars/3920

http://tips4mac.blogspot.com/2008/11/moon-phase-calendar-in-ical.html


Subscribe to the moon phase calendar with iCal. Then sync Now X to iCal. It won't have those nice pretty moon icons but it'll tell you the moon phases on certain dates.

BusyCal has built-in moon phases and built-in connection to AccuWeather as well. Sadly, you won't be able to transfer that to Now X because it is a BusyCal only feature.