The platform of the Arecibo Observatory telescope is a large triangular scaffolding structure that houses all the receivers and most of the front-end electronics for processing signals from the telescope. The platform is suspended from three towers surrounding the main dish, with each point of the triangle directly connected by cables to one of the towers. One can reach the platform either by taking a cable car up (maximum of 4 people at a time) or climbing the catwalk, an at times frighteningly flimsy walkway that guides you up the several hundred feet from the top of a cliff to the base of the platform (maximum of 5 people at a time).

Receivers for the telescope are located in one of two structures affixed to the base of the platform. The first is a large metal Gregorian dome that was just installed in 1997, and the second is what is known as the Carriage House, which is something of a holdover from the original receiver system implemented when the telescope was first built. A large arm attached to a circular track at the bottom of the platform allows both structures to rotate to different locations above the dish. As an observer rotates the receivers, he is actually steering the telescope to look at different parts of the sky by pointing at different parts of the dish. (More explanation about this later.) Observers can also position the receivers at different points along the length of the arm, giving him further steering flexibility.

Inside the dome are a variety of different receivers, each of which is attuned to a certain range of frequencies. Astronomers observing at the telescope may select from any of these receivers depending on what portion of the radio wave spectrum they are looking to study. Most commonly used is the L-band receiver which is centered on the 21-cm neutral hydrogen emission line. Radio waves are focused from the main reflector, up into a secondary reflector housed in the roof of the dome, down onto a tertiary mirror, and finally up into the receivers.

The Carriage House on the other hand makes use of a much more primitive technique for observing signals from a spherical reflector (such as the main dish of the telescope) by using a single line feed. The line feed corrects for the fact that spherical reflectors focus incoming rays to a line instead of to a point (the dome corrects for his using its complicated system of multiple mirrors). However, the line feed is only capable of viewing a very limited range of frequencies, whereas the dome's receivers tend to have a much broader range. Attached to the line feed are two different radar transmitters, which astronomers can point out into the sky in order to observe the reflected pulses and thus try to put together pictures of how far-off objects look in space. The Arecibo transmitter is the most powerful non-military-use radar in the world.

Beyond all of its nifty electronics, though, the platform of the Arecibo telescope is one of the most amazing places to visit in the world. Watching the huge structures rotate, and walking around 450 feet above the ground with little more than a grating to support you is just plain exhilarating (not recommended for people with a fear of heights). This tour in and of itself made a summer's worth of hard work at the observatory worthwhile. (Of course just the coolness of being in Puerto Rico made it worthwhile, but this was icing on the cake.) Wow.

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