Scientists study Anasazi calendar

And they discover it more advanced than previously suspected.

Dr. Don Smith/College of Eastern Utah, San Juan Branch: "I think we're becoming more aware that those people were far more familiar with astronomy, science and possibly math than we give them credit for."

That's probably why those who are amateurs or professionals - who study these sites- are called archaeoastronomers. The calendar markings are accurate every year. A photograph of spring equinox from last year - right on target - the ancient target that is.