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The largest radio telescope in the world and the one used
for the Berkeley SETI search is the
Arecibo
Radio Telescope
, in northwestern Puerto Rico, near the town of Arecibo.
The telescope has a fixed dish 305 meters (1000 feet) across that is built
into a sinkhole in rugged Karst terrain. To imagine how big this dish is,
it would take 10 billion normal bowls of cereal to fill the radio dish to
the brim! Still hard to imagine? The large surface of this dish is over
18 acres or 26 football fields in area! The dish reflects and concentrates
the weak celestial signals on the receiving antennas hung 450 feet above.
Since the dish is fixed and can't swivel, the receiving antennas are mounted
on a bow-shaped track that allows them to "look at" objects as
far as 20 degrees from the zenith (directly overhead). This bow-shaped arm
is itself mounted on a circular track to allow the antennas to follow an
object as it moves across the sky due to the earth's rotation. These two
motions give the telescope the ability to scan a good portion of the sky.
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The high-frequency "Gregorian focus" is inside the dome. The lower
frequency 430 MHz line feed is the spear-like structure to the left of the
dome.
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T
he telescope has two main antenna systems: the lower frequency
430 MHz line feed, and the giant domed "Gregorian" focus. The
Gregorian is a new addition to the Arecibo Observatory. It allows more accurate
high-frequency (up to 10,000 MHz or 10 GHz) observations. Inside the dome
are two radio reflectors that will more finely focus the radio signals onto
the detectors. Although the dome may look rather small in photographs, it's
actually 85 feet in diameter!
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"SERENDIP: The Search for Life"
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