As they have for centuries, ancient ruins around the globe aligned with the sun this month. Like fine-tuned Swiss watches, they marked the solstice, indicating the beginning of summer in the northern hemisphere. Researchers and travelers are paying more attention to these archaeoastronomy sites, which operate like giant calendars to note the passing seasons.

"It's something human beings have always done. They were keenly interested in the patterns of nature," says Ken Taylor, author of "Celestial Geometry: Understanding the Astronomical Meanings of Ancient Sites" (Watkins Publishing, $19.95). He shares some notable destinations with Larry Bleiberg for USA TODAY. 

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