Last week, the National Radio Astronomy Observatory in Green Bank celebrated the 50th birthday of the 140-foot telescope.
During the festivities, scientist Frank Ghigo and visiting scientist David Hogg gave a presentation on the “birth” of the telescope and the initial discoveries made with it in the late 1960s, early 1970s.
When the NRAO was founded in the mid-1950s, the steering committee was discussing plans for telescopes and said the NRAO needed a scope that was at least 600 feet in diameter, Ghigo explained.
Instead, it chose to start small and settled on a 150-foot telescope.
“At the time there were sixty-foot dishes and eighty-foot dishes and the thought was, ‘we’ll just scale up one of those to one hundred fifty-feet,’” Ghigo said. “‘We’ll ask a company to build it and it will be practically off the shelf. It’ll be built really quick.’ The steering committee asked for designs.”
The first design was submitted by Husband & Company of Sheffield, England. J.C. Husband designed the Jodrell Bank 250-foot telescope in England and was a consultant to the steering committee for the 150-foot.
“This is called an Altaz design – Az is for azimuth and that’s the direction around the horizon from the north and altitude is the angle from the horizon up in the sky,” Ghigo said. “It was the Altaz design, as opposed to the equatorial design, which you would put everything on a shaft that is parallel to the Earth’s axis, so you rotate the telescope around the Earth’s axis and follow the motion of objects across the sky due to the Earth’s rotation.”
While the Altaz design would have been easier and cheaper to build, members of the steering committee insisted on an equatorial design.
The committee went back to the drawing board and many changes were made.
“Apparently AUI [Associated Universities, Inc.] asked for a design for a forty-meter telescope, to the one hundred fifty-foot turned into forty meters,” Ghigo said. “Forty meters is about one hundred thirty-two feet. An unidentified government official insisted that any U.S. telescope had to be expressed in feet not meters, so the one hundred thirty-two feet was rounded up to one hundred forty. So it ended up being one hundred forty-foot diameter.”
With plans for a 140-foot equatorial design telescope, the NRAO had a groundbreaking dedication in October 1957 and construction began.
The NRAO planned for the telescope to be completed in four months, but the project met with many snags, delaying completion for several years.
“The contract to build the telescope was given to Bliss and Company of Canton, Ohio,” Ghigo said. “The contractors were paid four point seven million dollars to complete in four months. A year later, the pedestal structure was complete and they had these huge cranes for lifting up the major parts. This was kind of the view that was there for many years. The other components did not appear and did not get assembled on schedule.”
The main issue was the steel used for the structure.
“They found as they were welding the spherical bearing, lots of small cracks were forming on these small plates,” Ghigo said. “Eventually someone figured out the type of steel they were using was subject to what’s called brittle fracture which apparently means that at very low temperatures, the steel can catastrophically fail. That doesn’t sound good because in Green Bank, we do get low temperatures every winter. This became a problem.”
The polar shaft which was delivered to the site by train was also made with the faulty steel. It was abandoned and, according to Ghigo, the piece is buried somewhere on the site.
Only one piece made by Bliss and Company was used in the final telescope, except the base which was already built.
“The super structure was made of welded aluminum and this is the part of the Bliss Company design that actually worked to the proper specifications and was used in the final telescope,” Ghigo said.
While the delays and construction issues caused a lot of growing pains for the NRAO, they also paved the way for the 300-foot telescope. While the observatory was waiting for new and usable pieces for the 140-foot, the astronomers were afraid the idle facility would close. To ensure it would not fade into obscurity, the observatory planned the construction of the 300-foot.
“It was clear this project was going to be way over schedule – way late – and the astronomers at the observatory were worried that it was such a boondoggle at this point that the NSF [National Science Foundation] might just cancel the whole project,” Ghigo said. “So there was a lot of worry and the NRAO was not functioning as a national center the way it should, so the astronomers got together and said, ‘okay, can we build a large structure quickly that will put Green Bank on the map as a major radio astronomical center?’”
They did and the 300-foot telescope was completed in under two years.
“It did serve a purpose of making Green Bank a major center for radio astronomy, and so we like to think that the 300-foot really saved NRAO in a time when there was a lot of uncertainty,” Ghigo said.
The observatory returned its attention to the 140-foot telescope, with new project manager Max Small in charge and a new engineering firm, Stone and Webster, the project was back on track.
“A new polar shaft was built, following the new specifications,” Ghigo said. “All the major parts were brought by rail to Bartow and then brought by truck from Bartow here to the site.”
The telescope was completed in 1965 and the astronomers began using it to observe the night sky.
As a visiting scientist, David Hogg used the telescopes at the observatory in the late 1960s, early 1970s.
It was a time of excitement and stress. Astronomers were excited to have a new telescope to use and were stressed because it was finally time to prove the telescope was worth all the effort.
“The project was over budget and much delayed, so 1965 was greeted with excitement and apprehension,” Hogg said. “We could finally get to test out the telescope, but would it be good enough. It wasn’t a long shot though, because there are three great advantages that NRAO and AUI have – there was a strong management team in place, the technical support at the observatory was pretty strong and the operations group was highly experienced.”
It didn’t take long before it was obvious the telescope was a success.
“There’s not suspense to this story, right?” Hogg said. “The telescope worked and it worked well. What I want to do is describe how well it worked. It gave us a new way to view the universe and I want to persuade you that’s true. It’s a very important statement. Stop and think about that. A new way to see the universe here in Green Bank with the 140-foot.”
Hogg shared a slide in his presentation showing the first observations of radio recombination lines.
“What I am showing you here is the strength of the radio signal as a function of frequency across the radio band,” he said. “The fact the signal goes up here at the predicted point means that we have found the signal given off by hundreds of nano electrons captured. Here in this great ionized hydrogen region within the Milky Way and it’s here in the Orion Nebula, one of the famous viewing features in the winter sky. They also looked at two bright radio sources – the Crab Nebula which – is a supernova and they looked at the extra galactic radio source, a couple of colliding galaxies. Very powerful.
“Radio astronomy flies blind unless it can get an optical identification,” he continued. “You’re not really sure what you’re looking at, but with a spectral line like this, you can measure its distance. You can see how it’s being shifted by motion. With this detection we can now start to map the regions where hydrogen was in the Milky Way.”
The 140-foot continued to assist with discoveries. In 1968, astronomers discovered an emission of the ammonia molecule and formaldehyde, the first Milky Way outer space organic complex molecule.
It became a competition to use the 140-foot and observers tried to keep their projects secret from one another.
“Observers jockeyed for telescope time on the 140-foot,” Hogg said. “Since this was the telescope of choice with which to observe the large molecules, everyone wanted to use it. The observers would swear the technicians to secrecy over what frequency they were using. They would put notes on the blackboard of what molecules they were seeing, but of course, the notes were completely false. They weren’t looking for those molecules.”
It may have been a stressful time, but the excitement of discoveries lightened the stress and drew the attention of astronomers from all over the world.
After the presentation, the celebration was moved to the lawn underneath the 140-foot, where visitors enjoyed a picnic, as well as tours of the telescope and an exhibit sharing memories from the past 50 years.
NRAO site director Karen O’Neil spoke about the 140-foot telescope and what is in store for it in the future.
“We did this not only for the celebration of the fiftieth birthday of the 140-foot telescope, but we’re actually going to start having tours going through the telescope, too,” she said. “All those exhibits, you guys are the first to get to see them. This is going to be something new that the EPO group is leading.
O’Neil said the majority of the items for the exhibits were collected by Ellen Bowden in Charlottesville, Virginia.
O’Neil also reflected on how the state’s perception of the NRAO has changed over the years.
“I should say that when I was a kid growing up in West Virginia, the NRAO was something that you kind of knew about and it was just kind of what it was,” she said. “I never visited here. I’ve really seen that change immensely. It started to change in the 70s, but it’s really turned around a lot and the state of West Virginia notices us. In fact when they heard about the fact that this was the fiftieth anniversary of the 140-foot, they actually went ahead and passed a proclamation by the state of West Virginia.”
The proclamation stated that the 140-foot will forever be recognized as one of the premiere instruments at the NRAO in Green Bank. It was in operation for 36 years and remains the largest equatorially mounted telescope in the world.
Although the day was a celebration of the 140-foot, it was also a celebration of the NRAO as a whole. In that regard, O’Neil and fellow employees opened the 300-foot telescope time capsule.
“This was buried in September 1987 and we just pulled it out the other day,” O’Neil said. “The plaque reads, ‘on this day the time capsule is buried beneath this plaque. Please uncover it in 2012 for the 300-foot telescope’s golden anniversary.’ Unfortunately, the 300-foot only lasted three months beyond this time capsule and also unfortunately, on September 2012, we were kind of worried about a few other things, so we let this slide and we figured the fiftieth birthday of the 140-foot was a good time to open it instead.”
Included in the time capsule were manuals, spec sheets, photos and technical parts. O’Neil said some of the items will go into the archives while others will remain in the time capsule, which they plan to bury at the 140-foot telescope site.
The event culminated with a screening of the films “The Lift” and “The Making of the 140ft Telescope.”