Arecibo Radio Telescope 1963-2020

Part of the Arecibo radio telescope collapsed this summer. A supporting cable had snapped.

Another cable gave way this month.

I’d like to be writing about plans to repair the dish, replace aging cables and restore the historic observatory to usefulness.

Instead, I’ll be taking a quick look at the Arecibo observatory’s origin and achievements. Make that achievements of scientists using the radio reflector.


What? No Space Alien Conspiracies?

‘There’s never a crackpot around when you need one!’

The Arecibo radio telescope started bouncing signals off planets and listening to radio waves from the stars in 1963.

Finding reliable information about the facility’s technology and science was easy.

But my quest for good conspiracy theory was an effort fraught with frustration and ultimately futile.

I found a few offhand mentions of ‘many’ conspiracy theories whirling around the big dish. Several quick searches this week uncovered a bogus crop circle near the Chilbolton radio telescope, back in 2001. And that’s it.

And I found that while checking out the “Arecibo message:” a 1974 technology demo. Or publicity stunt.

The Arecibo message is real enough. It’s a digital 73 by 23 raster cooked up by Frank Drake, Carl Sagan and others. The idea was that space aliens could decode it.

Maybe so, but I think it’s anyone’s guess how they’d interpret the 1,679 pixels. Maybe I’ll talk about that some time. Then again, maybe not.


Sic Transit Gloria Arecibo

A Professor, Sputnik and an Act of Congress


(From University of Central Florida, via BBC News, used w/o permission.)

Iconic Puerto Rico telescope to be dismantled amid collapse fears
Paul Rincon, BBC News (November 20, 2020)

The iconic Arecibo radio telescope in Puerto Rico is to be dismantled amid safety fears, officials have announced.

“A review found that the 305m telescope was at risk of catastrophic collapse, following damage to its support system.

“It concluded that the huge structure could not be repaired without posing a potentially deadly risk to construction workers….

“…Sethuraman Panchanathan, director of the US National Science Foundation (NSF), which funds the telescope, said in a statement: ‘NSF prioritises the safety of workers, Arecibo Observatory’s staff and visitors, which makes this decision necessary, although unfortunate.’…”

The facility’s official name is National Astronomy and Ionosphere Center, NAIC.

Its nickname, Arecibo Observatory, refers to Arecibo, Puerto Rico: a town about six miles north of the radio dish.

The observatory’s story starts about six decades back. Cornell University’s William E. Gordon was studying Earth’s ionosphere in the 1950s. He figured that he’d learn more by bouncing radio waves off it, and started pushing for a big radar reflector.

The Cold War was in progress. Sputnik’s successful launch prodded America’s government into taking satellites and ballistic missiles seriously.

Congress passed the National Aeronautics and Space Act in 1958. That legislation launched NASA and ARPA: the National Aeronautics and Space Administration and Advanced Research Projects Agency.1

And, thanks to W. E. Gordon’s ionospheric interests, the Arecibo Observatory.

World’s Biggest: 1963-2016


(From University of Central Florida, used w/o permission.)
(Arecibo dish damage, August 2020.)

Professor Gordon pointed out that a thousand-foot-wide radar dish would open a new window for astronomers. Metaphorically speaking.

With it, scientists could look for a ring current around our planet, bounce signals off Venus and Mars and even look for hitherto-unobserved “radio stars.”

The astronomical kind, not entertainers like Jack Benny and Edgar Bergen.

Gordon also said that maybe orbiting satellites would leave an ionization trail. If they did, the thousand-foot radar dish could detect them.

Construction started in 1960. The Arecibo dish was finished in 1963.

Maybe something like the Arecibo Observatory would have been built without Cold War concerns. Eventually. But I figure that the theoretical prospect of tracking satellites helped get government support for Gordon’s massive antenna.

The NAIC dish was the world’s largest until China’s 500 meter radio telescope came online in 2016.2

An Unexpected Spin-Orbit Resonance

Less than a year after Arecibo’s first light, scientists found something unexpected. And, for many, unbelievable.

Astronomers had learned that Mercury is close enough to our star to be tidally locked.

Mercury could, and probably was, rotating in sync with its orbit 88-day orbit.

Observations of the planet seemed to confirm that one side of Mercury always faced our sun. Every time Mercury was far enough from the sun to be seen, astronomers saw the same features.

In 1964, Gordon Pettengill’s team said that they’d determined that Mercury rotated once every 59 days.

And infrared data from Mercury’s night side showed insufficiently cold temperatures.

Astronomer Giuseppe Colombo saw that Mercury’s Arecibo/Pettengill rotation value was roughly two-thirds of the planet’s orbital period. Colombo suggested that Mercury’s orbital and rotational periods had a 3:2 resonance, not 1:1. As it turns out, he was right.3

Pulsars, Planets and Prudence


(From University of Central Florida, used w/o permission.)
(Arecibo dish damage, August 2020.)

More discoveries came from the Arecibo dish:

  • 1968: First solid evidence that neutron stars exist
    • Periodicity of the Crab Pulsar (33 milliseconds)
  • 1974: First binary pulsar
    • PSR B1913+16
  • 1982: First millisecond pulsar
    • PSR B1937+21
  • 1989: First direct image on an asteroid
    • 1989 PB/4769 Castalia
  • 1990: Pulsar PSR B1257+12 discovered
    • Later found to have three planets
  • 1994: Mercury’s polar ice mapped
  • 2008: Prebiotic molecules methanimine and hydrogen cyanide detected
    • In starburst galaxy Arp 220
  • 2010-2011: Bursts of radio emission from T6.5 brown dwarf 2MASS J10475385+2124234
    • The first radio emission had been detected from a T dwarf

I figure there would be more, if a cable hadn’t snapped August 10, 2020. Followed by another giving way November 6, 2020.4

I’m sorry to see the Arecibo radio telescope go.

But I think NSF director S. Panchanathan is right. Safety matters. And restoring an aging radio reflector isn’t worth risking someone’s life.


Science, Safety and Greater Admiration

As far as I know, the Church doesn’t have rules against fixing radio telescopes. Or rules that say we must fix them.

We do, however, have rules about human life, science and safety.

Exposing someone to mortal danger without a really good reason is a bad idea and we shouldn’t do it. (Catechism of the Catholic Church, 2269)

Science and technology are good ideas, part of being human. If we’re doing it right, paying attention to this universe lets us experience greater admiration for God’s work. (Catechism, 3536, 282283, 341, 2293)

But ‘it’s for science’ doesn’t make risking someone’s health or life okay. (Catechism, 22932295)

I’ve talked about this sort of thing before, and probably will again:


1 Radio astronomy and politics:

2 Opening a new window:

3 Mostly Mercury:

4 Arecibo’s science highlights:

About Brian H. Gill

I'm a sixty-something married guy with six kids, four surviving, in a small central Minnesota town. I mostly write and make digital art. I'm only interested in three things: that which exists within the universe; that which exists beyond; and that which might exist.
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