The GBT
(Green Bank Telescope or as we like to call it – The Great Big Telescope)

A few weeks ago we had a great time in the mountains with our closest friends. We stayed in their cabin along the Greenbrier River in Pocahontas County and had the opportunity on Saturday to travel and do the “tourist thing”.

One stop was at the National Radio Astronomy Observatory in Green Bank. I have so many great memories of this facility. I worked at Watoga State Park in the late 1960s as Park Naturalist. Green Bank was one of the nature tour destinations that the park provided its guests. This was a time when the largest telescope at Green Bank was a large radio telescope affectionately known as “The Big Ear”. The Big Ear was Green Bank's 300-Foot telescope, that almost 100-meter dish, operated for over 25 years. Sadly the Big Ear collapsed in November of 1988 in a mass of rubble. Before it was destroyed, it was the largest telescope on the site. The radio dish, however, was not fully steerable and incapable of access to the entire sky. Through the years I have been on many great field trips to NRAO with students and teachers.

Now to the present and an even more impressive telescope. The GBT was completed in August of 2000 at a cost of $74.5 million and is the world's largest fully steerable radio telescope. It’s dimensions and complexity are astounding! The GBT is a 100-meter telescope, but the actual dimensions of the surface are 100 by 110 meters. The main dish is so large that it could house a football game. A system of lasers can fine-tune the pointing accuracy of the telescope with an accuracy of 1 arc-second. That is equal to the width of a human hair seen 6 feet (1.8 meters) away.

Wind, heat and cold, as well as gravity, can play havoc on the shape of the radio telescope dish. To counter this, small pistons adjust the exact position of the 2004 metal panels that comprise the dish. The shape of the huge dish is monitored continually by a network of laser beams trained at various spots on the dish's surface.The overall structure of the GBT is a wheel-and-track design that allows the telescope to view the entire sky above 5 degrees elevation. The track, 64 m (210 ft) in diameter, is level to within a few thousandths of an inch in order to provide precise pointing of the structure while bearing 7300 metric tons (16 million pounds – the same as 19 Boeing 747’s) of moving weight. The telescope weighs over 30 times more than the Statue of Liberty. The GBT is taller than the Statue of Liberty and about as tall as the Washington Monument. It is a truly amazing scientific instrument!