A Meridian Solar Calendar
The nearby 38 foot utility pole and rock alignment serves as a reminder of another ancient method of tracking of the seasons. This type of calendar uses a beam of sunlight or the length of the shadow cast by an object when the Sun is directly south at local apparent noon (as the Sun crosses the meridian or mid-point in the sky). At this moment the shadow points directly north. With minor adjustments this type of device can be used as a sundial to monitor the hours in a day.
Evidence suggests that the Anasazi, the Ancestral Pueblo Indians of the southwestern United States, used the interplay of a beam of sunlight and rock art to monitor the seasons in a similar fashion. Many European churches employed the beam of sunlight technique for calendar construction. In the 13th century the Chinese astronomer, Guo Shoujing, used the shadow method to determine the length of the year to the nearest minute. Early pioneers in this area noted local apparent noon with the saying, 'When the horse walks on the shadow of its belly, it's dinner time!'
At local apparent noon on the first day of Summer, the top of the utility pole's shadow falls on the boulder marked C (15 feet from the base of the pole). On the first day of Winter the shadow stretches to 100 feet and reaches the farthest boulder marked A. On the first days of Spring and Fall the top of the shadow touches the boulder labeled B (38 feet from the pole). This photo was taken at 12:00 p.m. on the first day of Fall, approximately 1½ hours before local apparent noon.
This meridiana constructed by Egnatio Danti in the 16th century at the Torre dei Venti (Tower of Winds) in the Vatican shows a beam of sunlight (enhanced) shining through a hole in the south wall at local apparent noon and projected onto the floor. The position of the Sun's image on the calendar dates chiseled into the marble floor indicates the time of the year.