The Arecibo Observatory was built in 1963 by the U.S. Air Force under the initiative of Professor William Gordon in the Department of Electrical Engineering and his colleagues at Cornell. The initial funding was for the ARPA (United States Department of Defense (DoD) Advanced Research Projects Agency (ARPA) missile defense program.
Located in Barrio Esperanza, Arecibo, Puerto Rico, is the observatory’s main instrument was the Arecibo Telescope, a 1,000 ft spherical reflector dish built into a natural sinkhole, with a cable-mount steerable receiver and several radar transmitters for emitting signals mounted 492 ft above the dish.
In 1963 it was the World’s largest single-aperture telescope. 53 years later, in July of 2016, it was surpassed by the Five-hundred-meter Aperture Spherical Telescope (FAST) in China.
ARPA had sought a means to try to detect incoming missiles while they traveled through the ionosphere where the ionized part of Earth’s upper atmosphere,
from about 30 miles to 600 miles altitude, is ionized by solar radiation. It plays an important role in atmospheric electricity and forms the inner edge of the magnetosphere.
The magnetosphere is a region of space surrounding an astronomical object in which charged particles are affected by that object’s magnetic field.
Besides studying the ionosphere it was realized that the telescope could study, what was then the new fields of radio and radar astronomy. Its surface is made of 38,788 reflective aluminum panels, each 3 feet by 6 feet.
The ground screen is 50 feet high surrounding the perimeter of the primary antenna, the reflector dish. This screen has an area of about 16,000 square meters, the size of five football fields. The screen reduces radio noise emitted by the ground that gets into the receiver systems.
In 1997, doubling of the power of the transmitter, to 1 million watts from about 420,000 watts, used for radar studies of the solar system. The new transmitter combined with the telescope forms the world’s most powerful radar system. Results were images of remarkable resolution: about 1/2 mile for the surface of Venus, down to 50 feet for asteroids and comets. That is sensitive enough to detect a steel golf ball at the distance of the moon.
Unfortunately, cables that support the Arecibo Observatory have started to break. An auxiliary cable slipped out of its socket on August 10, 2010, and caused damage to the dish below.
Another cable, this time a main, broke under the new stress caused by the missing auxiliary cable causing more damage on November 6th, 2010. This caused tremendous stress on the remaining cables
causing the U.S. National Science Foundation (NSF) to announce, November 19, 2010, that the facility was to be decommissioned and disassembled safely. Soon after the remaining cables gave way and the dish below was destroyed. No one was hurt.
The collapse brings the illustrious career of one of astronomy’s most powerful instruments to a close. Over the past 57 years, Arecibo was a pioneer in a dizzying array of astronomical fields — observing pulsars and fast radio bursts, tracking potentially hazardous near-Earth asteroids, and even searching for extraterrestrial intelligence. It also revealed that Mercury only takes 59 days to complete its orbit around the sun, not 88 days as previously assumed.
A cool thing about the Arecibo Observatory is that, in addition to receiving radio signals, it can also transmit them. This capability was put to the test in 1974 when the facility beamed a transmission, known as the Arecibo message, to globular star cluster M13. This region of space is approximately 25,000 light-years away, so we’ll have to be patient about receiving a response. Written in binary, the message was short, depicting things like DNA, the human form, and even a digital representation of the Arecibo Observatory itself. I have placed the message at the bottom of this post.
The first binary pulsar — a highly magnetized rotating star orbiting another — was first discovered at the Arecibo Observatory by Joseph Taylor and Russell Hulse in 1974. The more exciting detail about this discovery was finding out that the orbit of the two stars was shrinking at a rate of 1 centimeter per day.
The shrinkage was attributed to the loss of orbital energy due to gravitational radiation — or gravitational waves — predicted by Einstein’s General Theory of Relativity. This discovery was crucial for testing the theories of gravity and led to both the scientists winning a Nobel Prize in 1993.
For a long time, scientists hypothesized that there had to be more planets in the universe than just the ones that existed within the solar system. But, evidence to prove that theory was scarce. That is, until 1992. That’s when the Arecibo Observatory was able to capture the very first exoplanet. In subsequent years, it was able to discover an entire planetary system around pulsar PSR 1257+12.
However, since Arecibo did not rely on optical images but radio waves, it was able to break through the haze and create the first-ever radar maps of Venus’ surface. This discovery led to the prospect that it may even be possible to map the surface of Venus at resolutions down to 2 kilometers.
There was also the detection of the first-millisecond pulsar, PSR B1937+21. It was discovered in 1982 by DC Backer, Shrinivas R. Kulkarni, Carl Heiles, MM Davis, and WM Goss. Spinning roughly 641 times per second, it remains the second fastest-spinning millisecond pulsar of the approximately 200 discovered after that.
NASA may have caught the first-ever photos of ice on Mercury poles, but that only happened in 2014. Observations from the Arecibo Observatory had already detected water on the North and South of the planet closest to the Sun over two decades earlier in 1992. It showed that the ice persists in Mercury’s shadowed craters despite the high temperatures of nearly 426 degrees Celsius on the planet’s surface.
Scientists first detected fast radio bursts (FRBs) in 2007, but two major factors prevented them from fully understanding these enigmatic, millisecond-long pulses. 1) They had (until recently) originated in galaxies far, far away.
2) They were fleeting, one-off events. That changed in 2016 when scientists working at the Arecibo Observatory spotted the first repeating FRB. It seems these pulses are coming from highly magnetic neutron stars known as magnetars.
Arecibo is famous for its use in SETI — the search for extraterrestrial intelligence. The observatory has been used by such groups as SETI@Home, the SETI team at the University of California, Berkeley, and the SETI Institute’s Project Phoenix.
The Arecibo Observatory was featured in the 1997 movie “Contact”. Carl Sagan conceived the idea for Contact in 1979. The American science fiction drama film directed by Robert Zemeckis starred Jodie Foster, Matthew McConaughey, James Woods, Tom Skerritt, William Fichtner, John Hurt, Angela Bassett, Rob Lowe, Jake Busey, and David Morse. Jodie Foster is Dr. Eleanor “Ellie” Arroway, a SETI scientist who finds evidence of extraterrestrial life and is chosen to make first contact.
In case you’re wondering, here’s what the Arecibo message looks like: