Stone pillars, moon’s 18.6-year cycle and ancient structures tell a story.. The major lunar standstill northern moonrise is visible between Chimney and Companion rocks once per month for a period of about 24 months, every 18.6 years.. To archaeo-astronomers, the stone pillars that give Chimney Rock National Monument its name and the structures there built by ancestral Puebloan people send a message. .... And something did happen at the monument Tuesday night: The moon rose between Chimney Rock and Companion Rock, demonstrating a rare celestial occurrence called the major lunar standstill. The event occurs monthly over the course of about...