A high-altitude observatory
On a limestone plateau near the 9,642-foot (2,939 m) summit of Medicine Mountain sits the Big Horn Medicine Wheel, a circular pattern of stones measuring roughly 82 feet (25 m) in diameter. The structure is composed of a central stone cairn about 12 feet across, from which 28 stone spokes radiate to an outer ring. Six smaller cairns are positioned around the perimeter of the wheel. The entire structure is made of local limestone, which builders would have carried to the summit.
In 1972, astronomer John Eddy published research demonstrating that the wheel functions as a celestial observatory. Specific pairs of cairns align with the sunrise and sunset on the summer solstice. Other alignments mark the heliacal rising, the first day a star is visible on the eastern horizon just before sunrise, of three bright stars. The alignments point to Aldebaran, Rigel, and Sirius. The heliacal rising of these stars occurs on predictable dates, allowing an observer to mark the passage of summer. For example, Aldebaran's rising signaled that the summer solstice was a few days away. The 28 spokes of the wheel correspond to the number of days in a lunar cycle, suggesting another layer of astronomical tracking.