Month and day optional?

I'm using the Date module with CCK and the book content type. I added a date field so that I can specify the date (insomuch as I know it) for specific events in a biographical chronology. The problem is that sometimes I know only the year, sometimes I know the year and month, and sometimes I know year/month/day. Is there any way of changing the parameters so that it allows me to have the option of entering the full year/month/day granularity, or just year/month or just year? (I think this means having month/date as optional) Right now, if I leave out month and day it defaults to "January 1st, XXXX" which is misleading in the biographical sequence.