Green Bank Observatory

A valley chosen for silence

The National Radio Astronomy Observatory selected Green Bank, in the Allegheny Mountains, in 1956 after a search for a site shielded from radio interference; observations began in 1958. A National Radio Quiet Zone, covering about 13,000 square miles of West Virginia and Virginia, was established in 1958 to limit transmitters near the site. Even today, Wi-Fi and mobile phones are restricted close to the telescopes.

Green Bank was the home of Project Ozma, in 1960 the first search for radio signals from extraterrestrial intelligence, made by Frank Drake with the 85-foot telescope, listening to the stars Tau Ceti and Epsilon Eridani. In 1961 Drake presented what became the Drake equation at a meeting there.

A collapse and a new telescope

The 300-foot transit telescope, built in 1962 and used for sky surveys, collapsed on 15 November 1988 when a gusset plate in its structure failed without warning; no one was hurt. Congress funded a replacement, and the Robert C. Byrd Green Bank Telescope, a 100-metre dish, was dedicated in 2000.

The Green Bank Telescope's offset feed arm leaves the aperture unblocked, and its surface is made of about 2,000 panels that actuators adjust to correct for gravity and temperature. It is the largest fully steerable radio telescope in the world.

An independent observatory

In 2016 Green Bank became an independent observatory, separate from NRAO, operated by Associated Universities, Inc. with the National Science Foundation. The observatory carries on pulsar timing for gravitational-wave searches, as part of NANOGrav, and offers the telescope to astronomers worldwide; the Quiet Zone continues to protect it.

The cost of silence

Green Bank's radio quiet zone limits the use of everyday devices near the observatory, from Wi-Fi routers to microwave ovens, and residents have mixed views of it. Some people with sensitivity to radio waves have moved to the area, a phenomenon that scientists do not explain by the radio environment. For the observatory, enforcing the zone is a daily task, with a team that tracks down sources of interference. The experience shows that protection of the spectrum is a service that must be operated, not just declared, and that it has social costs that need to be addressed openly.

Instruments and technologies

• Green Bank Telescope A 100 by 110-metre off-axis paraboloid on an alt-azimuth mount, with an active surface of about 2,000 panels adjusted by actuators.
• 85-foot telescopes Early 26-metre equatorial dishes, used for Project Ozma and surveys.
• Radio Quiet Zone monitoring A fixed monitoring station checks for illegal transmitters and interference in the zone.

The people

• Frank Drake Radio astronomer who ran Project Ozma and wrote the Drake equation.

Timeline

• 1956 Observatory established.
• 1958 First observations made.
• 1960 Project Ozma, the first radio SETI search.
• 1988 The 300-foot telescope collapses in November.
• 2000 Green Bank Telescope dedicated.
• 2016 Becomes an independent observatory, separate from NRAO.

Key lessons for observation today

• Protect the spectrum, as well as the dish The Quiet Zone matters as much as the telescope. The radio spectrum around a sensor is a managed resource.
• Inspect structures, and plan for failure The 300-foot dish fell without warning; the replacement was designed with that lesson. Structural health monitoring is part of any large instrument.
• Active control beats passive stiffness The telescope corrects its surface in real time. Modern instruments combine sensors and actuators to keep their shape.

Sources

• Wikipedia, Green Bank Observatory
• Green Bank Observatory, 60 years of radio astronomy in Green Bank
• e-WV: The West Virginia Encyclopedia, Green Bank Observatory
• Wikipedia, Frank Drake