Arecibo Diaries: Location is Everything

Apr. 15, 2003

by Seth Shostak - Senior Astronomer

Puerto Rico Coast at first glance, Puerto Rico seems a strange place to eye the sky.

A tilted block of land guarding the eastern end of the Greater Antilles, this island boasts no soaring mountains on which an optical telescope could perch, nor an unpopulated outback that would suit the signal-sensitive ears of a radio array.

What Puerto Rico does have is geology and location.

Stretching across the islands northern edge from the suburbs of San Juan to the western town of Aguadilla is a bumpy, limestone terrain known as karst. Pockmarked from thousands of millennia of rain, the karst is a jumble of haystack hills and broad sinkholes. One of the latter, about 8 miles south of the coastal city of Arecibo, is a perfect natural dimple to house the worlds biggest single-dish antenna: the Arecibo radio telescope.

Cornell University, which built this instrument in the early 1960s, realized that Puerto Rico offers more than accommodating topography. The islands southern latitude (18 degrees north) ensures that Venus and other members of our solar system pass overhead a big plus for a telescope whose 1,000-foot reflector, aimed at the zenith, is far too large to tilt.

Twice a year Spring and Fall we come to Arecibo, to profit from its unrivaled sensitivity in our search for signals from other worlds and other beings. This time, our night-time observing shift will be from 5:00 pm to 8:00 am, somewhat longer than usual. The run lasts 2-1/2 weeks, which is a very healthy allocation on an instrument in constant and widespread demand by astronomers worldwide. Cornell now operates the observatory under a cooperative agreement with the U.S. National Science Foundation, and Arecibo is frequently busy with studies of pulsars, galaxies, and (as Madison Avenue would gush) a whole lot more.

Project Phoenix has been using Arecibo since 1998, and in that time hundreds of nearby star systems have been examined for microwave signals. Unlike other SETI experiments, Phoenix can drill down on its targets to maximize the chances of picking up truly faint emissions. If an extraterrestrial broadcast breathes as much as 0.00000000000000000001 watts onto Arecibos 18-acre reflector, we could detect it. Thats a billion times fainter than kisses blown across a stadium.

Im packed and prepped for April in Arecibo, but my connecting flight to the island is hung up in Dallas. An ornery fuel valve necessitates an extra stop, and many of the passengers are peeved. I try to remain philosophical. After all, in November, 1493, when Columbus first stumbled upon the island, it had taken him 40 days to bridge the Atlantic from Cadiz to the Caribbean, a distance roughly comparable to the mileage from California. Despite the delays, my trip is still a hundred times faster than his. Watching the iridescent towns of the Bahamas slide by in the dark waters below, it strikes me how five centuries an eye blink in the history of humanity has changed Puerto Rico from an island awaiting discovery to one from which discovery is made.

The plane bounces onto the tarmac in San Juan, and the windows immediately fog up from the humidity. Once outside, I find the evening air a pleasant 77 F. Soon, Im stuffed into a rental car with fellow astronomer Mike Davis, his wife Jean, a small dog, and an impressive collection of luggage. We snake our way out of the airport, and ease on to the freeway to the west. It takes just over an hour to reach the small, labyrinthine roads that lead to the observatory.

Somewhat after midnight we pull into the observatory gates, and I collect my cabin key. The coquis thumb-size frogs with watermelon-size throats are out in force, lacing the humid air with their familiar ko-kee calls. In the near distance, the tracking motors of the telescope grind and groan. I find my way to bed.

The morrow will bring work, yes; but also promise.