Observatory at Arecibo: July 26, 2013

You might have seen the radio telescope at Arecibo in the film "Contact" with Jodi Foster or in "Golden Eye," the 1995 James Bond film.  The main collecting dish is 1,000 ft (305 m) in diameter, constructed inside the depression left by a karst sinkhole.  It contains the largest curved focusing dish on Earth, giving Arecibo the largest electromagnetic-wave-gathering capacity.  The dish surface is made of 38,778 perforated aluminum panels, each about 3 by 6 feet (1 by 2 m), supported by a mesh of steel cables.

Scientists are capturing radio signals from outer space here.  They don't want your Tweets!

Radio signals captured in the stationary dish, which is 1,000 feet wide, are bounced up to the mobile dome suspended above the dish.

Suspension cables help hold the dish in place in the sinkhole.

My first official senior discount.  Had to show my driver's license to prove I was 60.  Kind of like being 21 again . . . .

Summer rain is already falling.

Papa Tom at the Arecibo Observatory

The telescope has three radar transmitters, with effective isotropic radiated powers of 20 TW at 2380 MHz, 2.5 TW (pulse peak) at 430 MHz, and 300 MW at 47 MHz.

The telescope is a spherical reflector of radius 870 ft, not a parabolic reflector. To aim the telescope, the receiver is moved to intercept signals reflected from different directions by the spherical dish surface. A parabolic mirror would have varying astigmatism when the receiver is off the focal point, but the error of a spherical mirror is the same in every direction.

The receiver is on a 900-ton platform suspended 150 m (500 ft) above the dish by 18 cables running from three reinforced concretetowers, one 110 m (365 ft) high and the other two 80 m (265 ft) high, placing their tops at the same elevation. The platform has a 93-meter-long rotating bow-shaped track, called the azimuth arm, carrying the receiving antennas and secondary and tertiary reflectors. This allows the telescope to observe any region of the sky in a forty-degree cone of visibility about the local zenith (between −1 and 38 degrees of declination). Puerto Rico's location near the equator allows Arecibo to view all of the planets in the Solar System, though the round trip light time to objects beyond Saturn is longer than the time the telescope can track it, preventing radar observations of more distant objects.

Yes, the sign says "you will walk about 500 steps uphill."  We did.  Then, we walked 500 steps downhill in the summer rainstorm.  They weren't kidding about "Bring an umbrella in case it rains."