National Radio Astronomy Observatory - Green Bank, WV
My sister and I took a trip to the NRAO, Green Bank West Virginia facility earlier this month. I was hoping it was going to be a clear day, and it was when we started off from the Massanutten Resort, near Harrisonburg, VA. But as we snaked our way westward it got cloudier and colder. We even had some snow flurries.
The visitor’s center was nice, and we got some lunch before going on the tour. The small exhibit area was very nice including a huge concave mirror which focused the heat from a small lamp so you could feel it when you held your hand at the focus. Haul that baby outside and you could probably fix yourself a nice solar grilled steak, but not that day. They even had a monitor displaying the current sky. The used an earlier version of the free program Stellarium, than I use.
Jansky’s Antenna
They have a number of radio telescopes including a model of Karl Jansky’s antenna with which he discovered radio emissions from the heart of the Milky Way in 1933. They have the actual pioneering radio telescope by Grote Reber, a home made 31 foot diameter radio telescope built in 1937, a prototype of just about every radio telescope since. I particularly liked the Model T rear axle used as part of the manual azimuth positioning system.
Reber’s Radio Telescope with inset of the Model T rear axle
The above telescopes are for display. Other telescopes are a 40 foot telescope for student and amateur use. There’s even an operation manual for it on their web site. If you’ve wondered how you can observe with a radio telescope, that’s a good start.
There’s a 45 foot radio telescope that monitors for solar radio bursts, and is also used as a tracking station for Very Long Base Interferometry satellites.
There were three radio telescopes that looked very familiar to me. Three 85 foot radio telescopes set up in the straight line. They can be used as an interferometer to create more detailed observations of distant objected. They are of the same design and made by the same company as the University of Michigan’s radio telescope at Peach Mountain near Ann Arbor. (Note to non-Michiganders: There are no real mountains in the Lower Peninsula) They are on, what seems to be a rather ungainly equatorial mounts.
The largest equatorial mounted radio telescope is also there. A 140 foot telescope. While most radio telescopes look rather spindly, this baby looks massive. According to the web site, its back out of retirement.
The pride of the observatory was that largest steerable radio telescope in the world. It had a 300 foot diameter and was steerable only north and south along the meridian. It was in service from 1962 to 1988 when it collapsed due to structural failure.
This telescope was eventually replaced by the Robert C. Byrd Green Bank Telescope (GBT), the pride of the observatory. The main disk is a slight ellipse 361 by 328 feet approximately. Our guide didn’t know, but the reflector above the receiver cabin, is concave. This telescope is an off axis Gregorian telescope. This allows a clear aperture which reduces noise. On top of the receiver cabin is a turret with several feed horns, which can be switched out rapidly. The amplifiers there are cooled by liquid helium to reduce thermal noise in the system. Closeup pictures of the telescope can be seen near the bottom of this page: http://www.cv.nrao.edu/course/astr534/RadioTelescopes.html
GBT in maintenance position
When we were there the telescope was just finished being worked on by the maintenance crew. Apparently something needed fixing, since this was an observing day, rather than being down for scheduled maintenance. Our guide said that the telescope was high maintenance. As soon as the elevator, shown above the trucks in my photo below, reached the ground and the maintenance personnel got out, the telescope began rotating to point to some unseen celestial object above the clouds.
GBT from the east
If you’d like to visit the observatory, or want more information, check out http://www.gb.nrao.edu/
