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Reber Telescope

Original Reber Telescope, built in Wheaton, IL, and reinstalled in Green Bank.

Grote Reber

Grote Reber was born in Chicago on December 22, 1911 (d.12/20/2002). He was a ham radio operator, studied radio engineering, and worked for various radio manufacturers in Chicago from 1933 to 1947.

He learned about Karl Jansky’s discovery (1932) of radio waves from the Galaxy (i.e., the Milky Way), and wanted to follow up this discovery and learn more about cosmic radio waves. Were the waves coming only from the Milky Way, or from other celestial objects? What process produces the radio waves?


Tatel Telescope

When the NRAO was first founded, and the Green Bank site was chosen, the United States’ new national radio observatory had no radio telescopes. Plans for a giant telescope were underway, but no working telescope was on site. An order was placed with the Blaw-Knox Corporation in Pittsburgh, Pennsylvania for the purchase of one of their new 85-foot dish telescope kits. In the meantime, a 12-foot replica was used to test receivers and feeds for the 85-foot’s imminent arrival.

The kit arrived in summer of 1958, and the telescope was completed in early 1959. It was dedicated on October 16, 1958 and named in honor of Howard E. Tatel. Tatel designed the giant gearing of the telescope, presenting a scale model to Blaw-Knox that used his wife’s cereal bowl in place of the 85-foot dish. The new design increased the precision of the telescope’s movement and also made the kit much more affordable.

The Tatel Telescope began 24-hour a day observations on February 13, 1959, starting with the brightest radio objects known: Cygnus A, Cassiopeia A, and Taurus A. One of the first major observing projects performed was the first detailed mapping of the center of our Milky Way Galaxy by staff astronomer Frank Drake. He discovered that the heart of our Galaxy contains several sources of radio waves and is a lot more complex than ever seen before.

In 1960, Drake initiated a two-month observing program on the Tatel which he called Project Ozma, after the Queen of Oz, to aim the big telescope on two of the nearest, Sun-like stars in our galaxy to listen for possible signals from extraterrestrial civilizations. He and his team observed stars Tau Ceti and Epsilon Eridani with a receiver tuned to the 21-cm line of hydrogen, the most common radio signal in the Universe. Despite a brief excitement over what later turned out to be an airplane, the project did not pick up any signs of intelligent life around those stars.

The Tatel quickly gave astronomers more accurate positions and brightnesses for known radio objects. Astronomers also used the Tatel to measure surface temperatures for Venus and the Moon. Studies were done of Jupiter’s radiation belts, the envelope of charged particles that are trapped in the enormous magnetic field of our Solar System’s largest planet.

In the mid 1960s, two more 85-foot telescopes were built to the same design as the Tatel to become the three-element Green Bank Interferometer (GBI). A succession of smaller, portable telescopes was added to the interferometer to give it another axis and turn it into an array prototype for what would become the Karl G. Jansky Very Large Array.
Radio interferometers help astronomers study the fine structure and positions of radio objects, because the separation of the telescopes creates a powerful binocular vision.

The precision of the GBI allowed it to make the first radio measurement that confirmed, to high accuracy, the prediction by general relativity of the bending of light (i.e. any electromagnetic radiation) near a massive body.
From 1978 to 1996 the Tatel, as part of the GBI, was operated by the USNO for studies of Earth rotation and monitoring of variable radio sources. From 1996 until October 6, 2000, the Tatel Telescope was in continuous use as part of the GBI, funded partly by NASA, for radio studies of X-ray and Gamma-ray sources.

  • Reflector: 85-foot diameter paraboloid;  Surface is 0.125 inch thick aluminum panels;  Surface area is 5700 square feet with better than 0.125 inch RMS tolerance.
  • Focus: 36 feet above reflector surface and 115 feet above ground; Carries 600 pounds of receiving equipment; position relative to paraboloid stable to 0.25 inch.
  • Mount: Equatorial (polar and declination axis, mutually perpendicular)
  • Declination Axis: Shaft is 40 feet long, 16 inches diameter;  gear is 40 feet diameter; Travel is 132 degrees total, 48 degrees north of stow and 84 degrees south of stow.
  • Polar Axis: Shaft is 23 feet long, 28 inches diameter; Gear is 48 feet diameter;  Travel is about 90 degrees either way from stow.
  • Drive Rates, Both axes: Slew is 20 degrees per minute; Scan is up to 4 degrees per minute.
  • Material: Painted steel superstructure.
  • Brakes: Electrical set and spring set hydraulic release.
  • Total Weight: 210 tons.
  • Pointing Precision: About 30 arc seconds (about a quarter at 600 feet).

45 ft

The 45-foot portable radio telescope at the NRAO in Green Bank was a 1973 replacement for the retired 42-foot radio telescope that had been hauled around Pocahontas County in West Virginia since 1967 as the outlying fourth member of the Green Bank Interferometer. 

Over its 15-year tour of duty in the GBI, the 45-foot was disassembled, packed, hauled to and reassembled in a few nearby locations in the county, most notably in Huntersville. It was critical in helping to prove that the proposed Very Large Array project would be feasible and an extremely valuable tool for astronomy. 

Antenna of All Trades
At the conclusion of its successful nomadic phase, the 45-foot settled on piers at Green Bank in 1988 where NASA converted it into a tracking station for orbiting satellites. 

GEOTAIL, a joint NASA-Institute of Space and Astronautical Science (ISAS, in Japan) satellite sent up to study the magnetic stream off of the Earth, was the first orbiting craft to benefit from the 45-foot’s space communications. The second was a Very Long Baseline Interferometry (VLBI) test satellite called SURFSAT-1, built by undergraduates and NASA’s Jet Propulsion Laboratory in California. 

In 1995 the 45-foot began to send NASA mission controllers the timing signals for orbital corrections, and also it received their scientific data.

In 1996, Comet Hyakutake C/1996 B2 raced across our skies, and the 45-foot was used to examine the molecular-rich ice ball for interesting chemistry.

In 1997, after the launch of Japan’s VLBI Space Observatory Program (VSOP, aka MUSES-B, aka HALCA) carrying an 8m radio telescope, space VLBI became a brief reality. The 45-foot and NRAO’s VLBA participated in creating the largest telescope ever used – over 60,000 miles across! Coordination with the VSOP mission ended in 2001.

In between its late 20th-century tracking duties, the 45-foot telescope conducted the Galactic Plane A survey, mapping the entire Milky Way galaxy in the microwave wavelengths of 8.35 GHz and 14.35 GHz frequencies. 

Solar Telescope
The versatile 45-foot was once again adapted for a new purpose: solar observing. Retrofitted, the 45-foot began taking daily spectral observations of the Sun from decimeter to decameter wavelengths in 2004. As the Green Bank Solar Radio Burst Spectrometer, this little telescope functioned as a state-of-the-art instrument for discovering and monitoring solar radio bursts until 2012.  It worked with a smaller partner antenna as the prototype for FASR, the Frequency Agile Solar Radiotelescope, a next-generation instrument for observing solar phenomenon.

45 foot telescope, historical image
45 ft telescope historical image (AUI/NRAO/NSF)


The 20-meter telescope arrived as a guest at our site in Green Bank, West Virginia in 1994.  The telescope was built by RSI, funded by the US Naval Observatory (USNO) as part of their Earth orientation observing programs.

Engineers in Green Bank built its receiver and installed it on January 11, 1995. The 20-meter observed with other telescopes to test its systems during the next few months, but had to give up some of its parts to help a twin 20-meter in Hawaii. By October 1995, the 20-meter was in regular operation by the USNO.

The USNO uses antennas around the world to measure small wobbling motions of the Earth’s polar axis and irregularities in the Earth’s rate of rotation with reference to positions of quasars (distant bright explosions in nuclei of galaxies). Quasars are the most distant point-like radio sources known, and therefore form a good set of stable reference points. This telescope network is part of the the International Earth Rotation Service (IERS) and supplies data needed for high accuracy world-wide navigation systems.

The data are also used for studies of continental drift and of atmospheric and oceanic currents, in collaboration with the NASA Geodetic VLBI program. Prior to the completion of the 20-meter, these geodetic VLBI experiments had been using telescope 85-3, part of the Green Bank Interferometer.

The USNO shut down their use of the 20-meter in June 2000 due to funding cutbacks. Although the Green Bank 20-meter is no longer used for the USNO project, USNO monitoring  of Earth rotation and motions continues using the NRAO VLBA antenna array as well as telescopes in Hawaii and Germany.

In 2008, an L-band frequency array receiver feed, destined for use on the Robert C. Byrd Green Bank Telescope, was installed and tested on the 20-meter. It successfully observed the radio emissions around the famous Cygnus X-1 black hole complex.

The 20-meter was refurbished in 2012 as the first radio telescope in the Skynet Robotic Telescope Network project run out of the University of North Carolina, Chapel Hill.

Old receivers formerly used on the 140-foot telescope were revived and adapted for use on the 20-meter, providing receivers sensitive to 1.3-1.8 GHz, and 8-10 GHz.

The 20-meter telescope is used for a combination of educational and research projects. Anyone may apply to use it.

Automated through the University of North Carolina’s Skynet program, it is in regular use for educational activities around the U.S. and around the world. Via Internet remote control, students use the 20-meter to observe the invisible Universe from their classrooms and homes.
In addition, students and teachers participating in the Pulsar Search Collaboratory program use the 20-meter to conduct follow up research on candidate pulsars found in archived Green Bank Telescope (GBT) data. Students have discovered several new pulsars and become published authors before they leave high school!

After the onset of the COVID-19 pandemic, the Observatory’s Radio Astronomer for a Day program began using the 20-meter, instead of the 40-foot telescope, due to its remote operating capabilities. If you’re interested in scheduling this virtual opportunity for your student group, complete this form or contact us at gro.y1696269288rotav1696269288resbo1696269288bg@sn1696269288oitav1696269288reser1696269288.

A project with Virginia Tech and West Virginia University has used the 20-meter to search for the mysterious “fast radio bursts”, flashes of radio energy that happen seemingly at random spots in the sky at random times. Many observatories, including the one in Green Bank, are trying to gather more information to understand what is making these signals.

Height: 85 feet
Weight: 150 tons
Receivers: 1.3 to 1.8 GHz and 8 to 10 GHz at the prime focus
Slew Speed: 2 degrees per second, each axis.
Surface Accuracy: 0.8 mm rms.
Focal Ratio (F/D): 0.43
Geodetic Position: 38 26 12.661 N.Lat, 79 49 31.865 W.Long. 

40 Foot Telescope

In 1961, a 40-foot telescope was ordered from Antenna Systems, Incorporated and delivered to our growing observatory in Green Bank, West Virginia. This inexpensive aluminum telescope took only two days to set up and began observations on December 14, 1961.
The 40-foot telescope can only move in one direction, up and down. It relies on the Earth’s rotation to swing it underneath the space objects it observes. With a control system designed and built by NRAO staff, on February 1, 1962 the 40-foot became the world’s first fully automated telescope.

The 40-foot provided us with an unmanned observing program focused solely on radio sources whose brightness changes over time. Its five-year mission observed eight radio sources every day: 3C 48, 3C 144 (Taurus A, aka Crab Nebula), 3C 218 (Hydra A), 3C 274 (Virgo A), 3C 295, 3C 358, 3C 405 (Cygnus A), and 3C 461 (Cas A).  As far as we know, it was the first completely automated telescope. After sitting idle for nearly 2 decades, the 40′ was recommissioned in 1987 as an educational telescope.

Cool fact: We repurposed the Tatel Telescope’s 1960 feed, which was created by Frank Drake for Project Ozma, the world’s first scientific search for extraterrestrial intelligence.

More than 1,500 students ranging from 5th graders to graduate students use the telescope to investigate the radio universe every year.

The updated 40′ manual is available as a PDF file.

Here is a program you can install to convert between local sidereal time ( also known as the Right Ascension over the 40 foot) and Eastern time.

Published research using 40 Foot Data
The fading of Cassiopeia A: On Astro-ph

Receiver bandpass: 1340 MHz to 1580 MHz