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WHAT ARE RADIO TELESCOPES?

21 JUNE 2024 | Myrto Terpsiadou

«The total amount of energy from outside the solar system ever received by all the radio telescopes on the planet Earth is less than the energy of a single snowflake striking the ground.»
-Carl Sagan, Cosmos

When we hear the word "telescope," we typically envision a cylindrical device that is used for observing distant objects. However, another category exists with a different mode of operation: radio telescopes.

Image 1: An optical telescope under the starry sky, with the Milky Way visible in the background.

Radio telescopes collect radio waves from space, much like optical telescopes collect visible light. But what exactly are radio telescopes, and how do they differ from conventional ones?

Astronomical sources in space produce radio waves, including stars, galaxies, nebulae, planets, and moons. In our solar system, the Sun is the primary source of radio waves, with Jupiter being the second most significant source. Celestial bodies emit electromagnetic waves, including radio waves, at frequencies from 3 kHz to 300 GHz, due to their high temperatures or magnetic fields. Radio telescopes can detect and collect these radio emissions, even if they are quite faint.

The First Radio Telescopes:

In 1932, Karl Guthe Jansky, working at Bell Telephone Laboratories, was tasked with identifying sources of static that interfered with radio telephony. Jansky invented the rotating directional antenna, also known as "Jansky's merry-go-round." This antenna consisted of dipoles and reflectors on a rotating platform that could receive radio signals at a frequency of 20.5 MHz. With a diameter of about 30 meters and a height of 6 meters, Jansky's rotating antenna recorded various signals. After many months of observations, Jansky categorized these interferences into nearby and distant weather phenomena, as well as "whistlers" of unknown origin. The "whistlers" had a period close to 24 hours, suggesting a celestial source. Comparing his data with other astronomical observations, Jansky concluded that the radio signals originated from the center of our galaxy, near the constellation Sagittarius. Thus, the first radio telescope was "accidentally" created.

Five years later, in 1937, Grote Reber constructed the first parabolic dish radio telescope, 9.4 meters in diameter, in his backyard in Illinois. The radar technology developed during World War II was subsequently applied to radio astronomy.

How Do They Work?

Radio telescopes are comprised of the following components:

Dish: A large parabolic dish, similar to satellite TV antennas but much larger. It collects and focuses radio waves at a focal point.

Image 2: The 64-meter radio telescope at the Parkes Observatory, as it was captured in 1969. Retrieved from Wikimedia Commons.

Receiver & Amplifier: Located at the focal point, the receiver collects weak signals, which the amplifier then boosts. High frequencies are converted to lower ones for easier analysis.

Image 3: Diagram of a radio telescope showing the parabolic antenna, amplifier, and computer recorder, illustrating the process of receiving and processing signals. Retrieved from lecture notes of the University of Cincinnati.

Signal Processing System: This system separates the desired signals from unwanted frequencies. Then, analog signals are converted to digital for easier analysis.

Computer: The digital signals are converted into data that is analyzed and stored.

Motion Mechanism: Allows the radio telescope to point in any direction, collecting a wide range of data and tracking moving objects in space.

Control Room: A room where scientists operate the telescope and analyze the collected data.

Radio Telescopes vs. Optical Telescopes

Radio telescopes offer several advantages over conventional optical telescopes:

24-Hour Observation:
Unlike optical telescopes, radio telescopes can observe both day and night.

Unaffected by Weather:
Radio telescopes can "see" through clouds and rain, unlike optical telescopes which are affected by weather.

Invisible Objects::
Radio telescopes can gather information about objects in the universe that optical telescopes cannot detect, such as objects hidden behind stellar dust, nebulae, and other bodies.

Editorial Review: Konstantinos Karathanas
Scientific Review: Konstantinos Karathanas
Translation: Konstantinos Karathanas

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