Fogonazos: Arecibo, the largest telescope on Earth

The Arecibo observatory is the largest single-aperture telescope ever constructed. It is distinguished by its enormous size: the main collecting dish is 305 m in diameter, constructed inside the depression left by a karst sinkhole. The dish is the largest curved focusing dish on Earth, giving Arecibo the largest electromagnetic-wave gathering capacity. The Arecibo telescope's dish surface is made of 38,778 perforated aluminum panels, supported by a mesh of steel cables.

It is a spherical reflector (as opposed to a parabolic reflector). This form is due to the method used to aim the telescope: the telescope's dish is fixed in place, but the receiver at its focal point is repositioned to intercept signals reflected from different directions by the spherical dish surface.

The receiver is located on a 900-ton platform which is suspended 150 m in the air above the dish by 18 cables running from three reinforced concrete towers, one of which is 110 m high and the other two of which are 80 m high.

The platform has a 93 m long rotating bow-shaped track called the azimuth arm on which receiving antennae, secondary and tertiary reflectors are mounted. This allows the telescope to observe any region of the sky within a forty degree cone of visibility about the local zenith. Puerto Rico's location near the equator allows Arecibo to view all of the planets in the solar system.

The Arecibo telescope has made many significant scientific discoveries. It also had military intelligence uses, for example locating Soviet radar installations by detecting their signals bouncing back off of the Moon. And it was used for the SETI program.

In 1974, the Arecibo message, an attempt to communicate with extraterrestrial life, was transmitted from the radio telescope toward the globular cluster M13, about 25,000 light-years away. The 1,679 bit pattern of 1s and 0s defined a 23 by 73 pixel bitmap image that included numbers, stick figures, chemical formulas, and a crude image of the telescope itself.

Unfortunately, if other sources of funding cannot be obtained, the telescope will be shut down in 2011. If the additional funding is not available, Arecibo's radar astronomy program will cease October 1 2008.