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August 27, 2016

The world’s biggest single-dish radio telescope always points straight up. The Arecibo telescope in Puerto Rico is built in a bowl-shaped depression, so it can’t turn from side to side. Instead, it looks straight up — at the point in the sky called the zenith — and it uses instruments atop the dish to track stars.

Arecibo isn’t the first observatory built to look straight up. Many centuries ago, the Maya and other cultures built observatories for tracking the Sun as it crossed the zenith.

To these cultures, the cardinal directions were sacred. And “straight up” was the fifth cardinal direction. That was especially true at latitudes where the Sun passed directly overhead at certain times of the year. From Mesoamerica, for example, it crossed the zenith a few weeks before and after the summer solstice.

In the city of Monte Alban, built by the Zapotec, one building contains a small room with a 15-foot tube to the surface. When the Sun passed through the zenith, it shone straight down the tube, filling the room with light. And a smaller tube illuminated a room at a Mayan city. These devices helped residents celebrate the Sun — and the sacred zenith.

And from the northern half of the United States, a couple of bright stars are passing through the zenith right now. From the latitude of about Denver or Kansas City, brilliant Vega crosses the zenith around 10 or 10:30 p.m. And from farther north, the slightly fainter star Deneb is at the zenith around midnight.


Script by Damond Benningfield

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