This episode is sponsored by Awesome Socks Club, a sock subscription for charity.

Click the link in the description to  sign up between now and December 11th to get a new pair of fun socks each month in 2021. [ intro ]. Back in August, we talked about how  the Arecibo telescope in Puerto Rico suffered some pretty serious damage, in part  thanks to two recently-collapsed cables.

And now, it’s time to say goodbye. On November 19th, the National  Science Foundation officially called for it to be dismantled. And on Tuesday, before they could  even get in there for demolitions, the telescope’s instrument  platform officially collapsed.

This is a huge loss for astronomy, since there’s nothing else quite like Arecibo. But looking back on the telescope’s 57-year  history, there’s also a lot to celebrate! Because this observatory  made some major observations,   including ones that rewrote the textbooks.

Coming online all the way back in 1963, the Arecibo telescope reigned as the  world’s largest single-dish radio telescope for five decades. The dish stretched 305 meters across — so big that it was built  inside a natural sinkhole. Almost 150 meters above that dish hangs  an 816-metric-ton suspended platform, where all of the radio waves beaming down from space actually got collected  after bouncing off the main dish.

So, while the dish itself was  stuck looking directly up, the platform could be steered to help  focus on different areas of interest. And that’s also the part  that collapsed on Tuesday. Arecibo’s sheer size meant it  could see the details in small, distant bodies out there in space, so long as they emitted or reflected  certain frequencies of radio waves.

So it’s had a lot of jobs over the decades, from studying part of Earth’s atmosphere to hunting for near-Earth asteroids. And it’s got quite a few discoveries to its name. Just a few years after its mission began, the Arecibo telescope revealed that our  model of Mercury wasn’t quite right.

Since Mercury is the closest planet to the Sun, astronomers figured that the Sun’s  gravity would have tugged so significantly on the planet that it ended up like Earth’s Moon. In other words, only one side of  Mercury would ever face the Sun. The length of a day would be the same as its year, or about 88 Earth days.

But thanks to observations with Arecibo in 1965, astronomers learned that Mercury actually  takes about 59 Earth days to rotate. That means that three days on  Mercury last exactly two years. Astronomers call this relationship resonance.

And it’s thought that Mercury got that way  because its orbit is pretty oval-shaped. So the strength of the Sun’s  gravitational pull changes significantly as Mercury goes around — being stronger when the planet is closer,  and weaker as it moves farther away. This causes a torque, which  forces Mercury’s day into a stable three-to-two resonance pattern.

Knowing this little quirk  is important for astronomers as they refine their models of planetary dynamics. And it likely would have taken us much  longer to figure this out without Arecibo. Meanwhile, Arecibo was also responsible for discovering the first confirmed  planets beyond our solar system.

In 1990, two astronomers were using the telescope to study the leftover core of a star  that went supernova, known as a pulsar. Pulsars shoot out beams of light, and they spin — so they’re like cosmic lighthouses. And the timing of their beams as  seen from Earth are super regular.

Except, this pulsar’s signal wasn’t as regular as the team thought it should be. And it turned out that was because  there were massive objects in the area, gravitationally messing with its timing. They were two planets!

And we now know there are at least three in orbit around this stellar remnant. Until that point, some researchers thought hunting for  extrasolar planets was a waste of time, because our technology couldn’t possibly find the tiny signals a planet would create. But these days, an astronomer can spend  their whole career dedicated to it!

And in many ways, Arecibo paved  the way for that kind of work. And even after that, Arecibo  wasn’t done with pulsars! The telescope has also called into question the  entire concept of reliable pulsar regularity.

Over the years, it’s observed a few pulsars  that appear to randomly stop and start pulsing. And the length of time each of these  intermittent pulsars spends “turned off” varies. It’s still a mystery how  abundant these objects are, and exactly why they act so weird.

And now, in Arecibo’s absence, we’ll have to look to other  telescopes for answers. In the end, we would have loved to see Arecibo keep going for years to come. Even though there are other  radio telescopes out there, this one held a special place in astronomy, and supported the work of  thousands of researchers and staff.

So, for now, farewell, Arecibo. And to all the researchers and engineers involved:  . Congratulations on almost  60 years of incredible work.

If you need a pick-me-up  after this telescope news, well, there’s always the Awesome Socks Club. It’s a charity sock subscription, where you get a fun pair of socks designed  by a different designer every month in 2021. And 100% of the after-tax profits go to decrease  maternal and child mortality in Sierra Leone, which is one of the most dangerous  places to be pregnant in the world.

To control inventory and reduce waste, you  can only subscribe until December 11th. And you can learn more at AwesomeSocks. Club. [outro].