Similarly to optical telescopes that collect visual light, focus it to a point, amplify it, and produce an image, radio telescopes do the same with radio light. They add another piece to the puzzle that is exploring the cosmos. Visible light is all us humans can see with our naked eyes, but there is much more than just visible light coming from a star, quasar, or nebula.

To understand how a radio telescope works, you need to understand what a radio light wave is. Radio waves are the least powerful, lowest frequency, and highest wavelength spectrum of light that humans have discovered. The wavelengths for radio waves can range from one mm to close to 10 meters! To put that into perspective, visible light ranges from .4 to .7 micrometers. Refer to the light wavelength chart below to visualise the difference in waves.

To collect the radio waves, we use a radio telescope. These telescopes are different from others in a few key ways. They are massive, they are incredibly susceptible to interference, they can work during most conditions, and they can send signals out. The telescopes are huge because of how long the radio waves are. In order to capture a clear image of something, you need a lot of data. Since the radio waves take up so much space, a large collection area needs to be created. This can look a few different ways. Many radio telescopes look like big satellite dishes that are built into the ground, others look like many smaller satellite dishes all lined up in an array. Pictured below are the arecibo telescope in Puerto Rico and the VLA (Very Large Array) in New Mexico. These are two very well known and frequently used telescopes. The Arecibo telescope uses one large dish to gather enough data, and the VLA uses many smaller dishes to gather enough data.

Radio telescopes are also very susceptible to interference. Radio waves coming from outer space are often incredibly weak by the time they arrive here to earth. This causes problems when people begin to use cell phones, watch television, or listen to the radio. Cell phones themselves emit radio waves that are billions of times more powerful than the radio waves as they enter our atmosphere. Because of the extreme sensitivity, radio telescopes are placed in places where there is little to no population. For example, the VLA in New Mexico is surrounded by mountains and hours from the nearest city. This allows the scopes to gather the faint cosmic radio waves without disruption from natural and manufactured radio waves.

For the purpose of this blog, I’ll explain how a massive dish radio telescope works. As light comes down from the cosmos, the massive dish on the ground focuses all of the light to a point. The dish does this because it is curved like a magnifying glass. The focused light is then bounced around in a gregorian dome. This dome will always focus the light to a single point. This is important because the dome actually moves. Since the dish is focused straight away from the surface of the earth, the telescope appears as if it cannot be directed at anything except for what the earth allows it to be directed at. This is infact false because the Gregorian dome moves around above the dish. This allows it to collect light coming from different parts of the universe. The focused light is then directed towards a receiver that filters out all non-radio light and the radio waves are collected.

With all of that technology and science that goes into collecting radio waves, the images collected are spectacular.