Is there a way to add the phases of the moon to an iPhoto calendar that I'm making as a christmas present?

I'm trying to finish a calendar as a christmas gift for my grandmother aunts and uncles. The last thing I need is to try and add moon phases, but I can't find anyway to do this. I tried adding it as a calendar on my computer, but iPhoto won't pick it up as an option to include in my project the way it does with my other calendars.