A thousand years ago, Ancestral Puebloans made their home in the desert southwest. Yesterday we trudged the trails they navigated a millennia ago as we explored Chimney Rock, a national monument celebrating Chaco culture.

These were sky-watching people, who learned that every 18 and a half years, the moon would rise between Chimney Rock (right) and Companion Rock, the two sandstone spires above. This alignment is made possible by a phenomenon known as Major Lunar Standstill, a time when the moon appears to pause for three years in its wobbly north-to-south cycle. 

It’s believed that the Great House Pueblo we visited today was constructed in 1093 A.D., during one of these times. Another one is happening later this year. I wish I could be here to see it.