Thirty Years on the 40-Foot Telescope

In the midst of celebrating the 60th anniversary of the Observatory at Green Bank, it’s easy to overlook another anniversary. July, 2017 marks the 30th anniversary of educational programs at the Green Bank Observatory. In July 1987, the Green Bank facility opened its doors to 27 teachers in an experimental two-week summer institute, designed to introduce educators to a national research center. I was one of them.

The Forty Foot Telescope has been at the heart of the experiences we’ve offered teachers and students at Green Bank. Built in 1962 to make repeated observations of a small list of radio sources, it is an unabashedly old-fashioned telescope:

  • Data is recorded on a chart recorder;
  • There is no feed horn, no cryogenics, no computer;
  • There is no tracking ability. The Forty Foot is a transit telescope.

And yet, it is one of the most useful and productive instruments in radio astronomy! It is certainly true that the Forty Foot Telescope serves more users annually than all of the NRAO plus GBO telescopes combined! Here are a few notable observing stories from my years with the Forty Foot Telescope.

During that first summer in 1987, teacher teams used the Forty Foot to make maps of the sky around Cygnus A and Virgo A, and to measure the telescope’s efficiency and beam shape. Our team decided to mimic the operation of the 300 Foot, nodding the Forty Foot north and south to collect more data in a shorter time-frame. As we nodded the telescope from north horizon to south, we noticed a huge bump in the chart recording trace. Excited to discover a huge radio source, we raced our chart recording back to the astronomers. They smirked a little bit and asked us to go back down to the telescope and see if it was still there. It was. As it was at midnight, at 3 AM, in fact every time we looked! That big bump occurred right as the telescope passed through the zenith. We had indeed detected a radio source, the Earth! We were picking up radiation from the ground. In that context did teachers learn about “spillover.”

We are not alone: Teachers mapping the Sagittarius A region in 1989 were startled to see the chart pen start jerking up and down…were they seeing rapidly fluctuating interference? They quickly switched on an audio speaker to hear a NutraSweet commercial originating, apparently, at the Galactic Center.

Sagittarius A: One summer, in the mid 1990s, both south limit switches failed and the telescope plowed into the ground. Rather than registering horror at this state of affairs, teachers and staff rejoiced alike because, at least for a short time, the Forty Foot could finally see the Galactic Center. (The Forty Foot’s southern limit is normally a frustrating ½ degree north of the true center of our galaxy, Sagittarius A.) Luckily, the hearty Forty Foot sustained no permanent damage.

We are not alone–Part II. In January 1997, Glenville State College students discovered a signal of short duration (1.5 minutes) at the celestial location of RA 20:32 and Dec. 39.5 degrees. The source persisted through several days of observing, occurring at the same sky location each day. Although Green Bank astronomers dismissed the signal as interference at first, its sidereal reoccurrence and the tenacity of the students soon had staff intrigued. Other observatories were asked about the phenomenon, and couldn’t identify it. Two weeks later the Glenville students returned to the Observatory, but this time to use the 140 Foot Telescope.

The signal was there!

Unfortunately, spectral analysis revealed a “spread spectrum” and the signal was eventually determined to come from a military satellite, which had a 2X sidereal orbit.

What’s that funny wire? For almost as long as the Forty Foot has been an educational telescope, Dan Reichart of UNC has been organizing his own educational camp. They rig up some pretty fancy recording equipment to the Forty Foot to digitize the signals. A few years back they noticed a weird little wire poking out of the drive controller rack. As the teams cycled through the telescope they played with this little wire, pulling on it, trying to tuck it back in. Eventually, under closer inspection, they realized it was a mouse tail!

Those first summer institutes were good ones. The Observatory has continued the Forty Foot Educational program and now, after 30 years, over 1300 K-12 teachers, 500 college faculty, and thousands of K-16 students have graduated from what has affectionately been called: “Radio Astronomy Boot Camp”.

Some of those teachers have started their own programs for students, and some of those students are now astronomers or young science teachers bringing their students to Green Bank.

Thanks to Rich Bradley for working hard in 1987 to make the Forty foot functional for the first groups of teachers, and the telescope mechanics for keeping it that way, Carl Heiles for inspiring us to observe neutral hydrogen, a true staple of our educational programs for teachers and youth, Bill Radcliffe (do you remember the time you single handedly took the front end off the telescope???), Nathan Sharp, and Dave Woody for coming to the rescue when the Forty Foot needed a technical swift kick, Skip Crilly for updating the telescope and getting rid of pesky RFI, and all of the astronomers who have enlightened teachers and students over the years.

Special gratitude goes out to Carl Chestnut, who was my Forty Foot partner in crime for many
years and who I miss daily.


A Forty-Foot Telescope Story, by Sue Ann Heatherly