Perhaps you remember the early years of this century, and the fascination that many people had over the dates of 1/1/01, 2/2/02, etc. For a while there it was old hat -- heck, every year you got a new one -- but people realized that the party was going to end on 12/12/12. So on that day, a lot of people on the Quiltart list did twelve twelves on their blogs.
After checking out several of those posts, I decided to run down to the studio and do one myself. And then my friend Uta Lenk left a comment on the blog, "Now wouldn't that be a new Daily Art project for 2013? 13 thirteens for thirteen - what - weeks, months?"
She has documented several on her blog, including photographing her special tree every day in different weather, light and seasonal conditions; and finding a specified color each day to photograph. This year she's taking a photo every day at high noon.
here and here and here. We both enjoyed it so much that her comment about the twelve twelves immediately led me to issue a challenge: we would do thirteen thirteens during 2013, posting every fourth Tuesday.