The Green Bank Radio Telescope

by Prasad Ganti

I drove for seven hours to see a radio telescope. Green Bank is in West Virginia, passing through a forest to reach a middle of nowhere valley surrounded by mountains. This is also an isolated place in terms of being a radio free zone. There are no cell phone towers in a radius of fifty miles. This allows the telescopes to capture the radio waves coming out of space. This helps in exploration of astronomical objects like distant stars, galaxies, black holes etc. To accomplish these goals, it is important to stay away from man made radio noise.

Astronomy traditionally has been confined to seeing the light emitted by heavenly bodies. Nineteenth century discoveries proved that light is only a small part of the spectrum of what is known as electromagnetic radiation. It was found later that infrared rays (heat), x-rays, ultra violet rays, gamma rays, microwaves, radio waves are all part of this same spectrum. Telescopes were being constructed to capture the radiation coming from outer space at different frequencies. The methods of capturing are different for different types of radiation. Radio telescopes capture the radio waves by using antennas and piping the signal to sensitive receivers study.

Starting after a full day’s work, it was late in the night by the time we reached our hotel close to Green Bank. Navigation was difficult. Assuming Google maps cannot help us due to paucity of cell phone towers, we took our handheld GPS receiver which directly receives signals from the GPS satellites in the space. Unfortunately, our hotel address could not be found in its database. We tried the cell phone as long as the signal was received. And thought of resorting to good old technology of using directions from paper. Fortunately, we were able to reach the hotel (which was kind of a rural and bucolic farmhouse) in pitch darkness. The signal from the last cell phone tower, and thereafter some magic software from Google maps carried us to our destination.

Green Bank Observatory has a group which monitors for man made noise and tries to eliminate. No microwave ovens are allowed, unless they are enclosed in a metallic cage called Faraday’s cage. This cage prevents radio waves from the oven to spread out. No digital cameras are allowed because they emit radio waves as well. I saw a smart family bringing in the good old film camera, while we were not able to take any pictures inside the observatory. Not even a fitbit watch was allowed inside.

Only diesel vehicles are used on the premises because gasoline vehicles have spark plugs which initiate the combustion. The spark plugs are known to emit radio waves. Diesel on the other hand ignites by compression. The radio receivers used in the telescopes are cooled to a few degrees above absolute zero. This is to cut out the radio noise generated by the receivers. As a result, the radio receivers don’t last for more than six months. There is a shop on the premises which constantly builds replacement receivers. It is easy to distinguish man made radio waves, which have discrete (some specific frequencies) against natural ones which have continuous frequencies. Regardless, they are very strict about minimizing man made noise.

My interest in radio astronomy was triggered by a very interesting collection of video lectures on radio astronomy by Dr. Felix Lockman who is an astronomer at Green Bank. It all started accidentally in the 1930s when Karl Jansky of AT&T Bell Labs while experimenting his radio antenna for communications that some radio waves were coming from a particular direction in the sky. This could not be man made. He found that these radio waves are coming from outside of our solar system. The picture below is a replica of Jansky’s antenna at the front of the observatory. It is only a monument, not part of a working telescope.

Replica of Karl Jansky's radio antenna

Replica of Karl Jansky’s radio antenna

Given below is a replica of a telescope built by another radio astronomy pioneer named Grote Reber. The dish moves up and down in vertical direction using the curves in the left and the right. The whole contraption moves on rollers in a circle on the ground. This way, the telescope can be positioned to see any specific part of the sky.It is only a monument, not part of a working telescope.

Replica of Grote Reber's radio antenna

Replica of Grote Reber’s radio antenna

There are several radio telescopes inside the observatory which is an area about 1-2 miles in radius. One of the telescopes, the 85 foot radio telescope was used by Frank Drake to study for possible life outside of our planet. He established SETI (Search for Extraterrestrial Intelligence), which has since moved from NASA funded venture to a silicon valley funded one. This is where Drake came up with his famous equation for the probability of finding life elsewhere in the Universe. The conclusion is that life is not unique to Earth, but should be present in other parts of the Universe. Although we have not found any yet.

The biggest telescope is the 100 meter giant whose picture is given below. It appears small because I took all the pictures included so far with my iPad pro. No digital equipment are allowed beyond this point. Because it is about 2 miles away, it looks small.

The 100m radio telescope antenna

The 100m radio telescope antenna

I now have a picture from the internet which provides a close up. The buildings in the foreground give an idea of the scale of this structure. There is a curve which helps move the telescope in the vertical direction and the whole contraption resides on rollers in a circle on the ground. It can be moved to point to any specific portion of the sky.

The 100m Green Bank Telescope, courtesy Green Bank Observatory

Huge telescopes like this one cannot be made as a single piece. Multiple panels are used, and each of them driven by a motor to correct for factors like gravity, wind, heat etc. to keep the telescope focused. Special white paint keeps the dish cool and reduces the radio antenna noise.

There are advantages of a radio telescope over optical ones. Light gets blocked by the interstellar dust, whereas radio waves just pass through. Due to this reason, clouds of hydrogen, ammonia, water vapor, organic chemicals like formaldehyde and acetic acid have been detected in interstellar space using radio telescopes, which would not have been possible using the optical telescopes. Also, the radio telescopes can be used during the daytime or during lower visibility. There is no peeping into a radio telescope. The antennas feed all the data received from the radio waves into a computer, which then converts it into a colored picture. This is pretty much how major optical telescopes are operated today.

The presence of organic chemicals in space, although no DNA or proteins have been found yet, means that life could be present in other parts of our Universe. After all, Drake may be right ! If there is any life in other parts of the Universe, it is my speculation that radio telescopes may detect it first.

To be fair to other telescopes, the hidden pictures of the distant stars and galaxies made using the radio waves, can be combined with images from the optical, the infrared and the X-ray telescopes to form a composite image in what is now termed as multi messenger astronomy.

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This entry was posted in Mid Summer 2019, Sidereal Times and tagged . Bookmark the permalink.

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