Clouds that obscured the Spring Equinox solar show at Dzibilchaltún Wednesday morning cleared in time to delight a huge crowd at Chichén Itza by late afternoon.

An estimated 14,000 people visited Yucatán’s most famous Mayan archeological site for the twice-a-year illusion — a feathered serpent seemingly taking shape out of light and shadow on the temple pyramid.

The illusion lasted about 40 minutes starting at 4:05 p.m. A form of undulating light could be seen on the railing of the temple’s main staircase. The effect is fleeting, but may return today if sunny conditions prevail.

The phenomenon happens just twice a year, at the beginning of spring and fall.

With information from El Universal