How Do Radio Telescopes Work?

Radio telescopes are specialized antennas equipped with receivers designed to detect signals from objects in space that are not made by humans.

Unlike everyday TV and satellite dishes that capture signals for entertainment, radio telescopes focus on signals from distant cosmic sources. These telescopes come in various shapes, such as large dishes or smaller frameworks arranged across vast landscapes. Regardless of size or form, a radio telescope generally consists of several key components. The dish, or antenna, is crucial, as its size and shape are determined by the frequencies it is built to detect and the level of detail astronomers aim to capture.

A large dish is necessary to collect faint signals from distant cosmic objects and focus them onto a subreflector above it. The subreflector redirects the signal to a detector, which amplifies it if necessary, and the data is recorded for future analysis.

Telescope Breakdown

In recent years, radio astronomers have developed large arrays of dishes that enhance the ability to gather detailed data about objects or cosmic events. The larger the array, the more refined the detail. Some of these arrays extend across vast distances on Earth. These arrays use the technique of interferometry to achieve highly detailed observations of radio-bright objects.

Interferometry Explained

While larger telescopes can capture brighter images with more intricate details, their size is ultimately limited. The level of detail a telescope can achieve also depends on its wavelength of operation. To achieve resolution comparable to the Hubble Space Telescope, a radio telescope would need to span several kilometers. To overcome this limitation, astronomers use a set of antennas positioned to observe the same object and combine their data using precise timing and supercomputing. The collected signals are processed and combined to create high-resolution images, mimicking the power of a telescope much larger than the individual antennas.

Avoiding Interference from Modern Society

Radio astronomy requires a highly "quiet" environment, meaning it needs an area free of interference from human-made radio emissions. While it's not necessary for people to remain silent near a telescope, the absence of artificial radio signals is crucial for clear observations. Finding a truly radio-quiet location is difficult, but there are a few spots on Earth where radio waves from space can be detected without the contamination of modern technology. These areas are highly valued by astronomers as they provide a pristine view of cosmic radio waves.

Do Cell Phones Interfere with Radio Telescopes?

Devices like cell phones, radio stations, and everyday objects such as doorbells, entertainment systems, and home computers emit radio frequencies that can disrupt the natural signals from space. The Earth's atmosphere also plays a role in absorbing these signals before they reach telescopes. To avoid radio frequency interference (RFI) and atmospheric absorption, radio telescopes are typically located far from cities and technological hubs. These remote locations allow astronomers to study cosmic radio emissions that would otherwise be obscured by human-made interference.

The Radio Telescopes and Arrays of NRAO

Dear Lykkers! Some of the most renowned radio telescope facilities are part of the National Radio Astronomy Observatory (NRAO). The Karl G. Jansky Very Large Array (VLA), located in the plains of San Agustin, New Mexico, consists of 27 linked antennas that observe the cosmos.

Far to the south, the Atacama Large Millimeter/submillimeter Array (ALMA) is situated in the high Andes. This array studies radio waves at millimeter and submillimeter wavelengths, allowing astronomers to detect emissions that would otherwise be absorbed by water vapor in the atmosphere. ALMA provides high-resolution observations of everything from the formation of planetary systems to some of the earliest galaxies in the universe.

Another significant array is the Very Long Baseline Array (VLBA), a globe-spanning network of radio antennas. Spread across the United States, as well as Hawaii and the U.S. Virgin-Islands, the VLBA acts like a near-Earth-sized telescope capable of incredibly detailed observations of distant objects.

SPIDER 230C 2.3 meter diameter compact radio telescope for 1420 MHz radio astronomy

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The Discovery of the Early Universe

One of the most significant scientific discoveries made using radio telescopes was the detection of the cosmic microwave background radiation, which provides a radio view of the early universe. In 1964, scientists Arno Penzias and Robert Wilson discovered a steady "hiss" of radio noise at a specific frequency, no matter where they pointed their antenna. This radiation was traced back to outside the galaxy.

This discovery confirmed a theory proposed earlier that the afterglow of the Big-Bang would leave an imprint on the universe. The radiation appeared as microwave energy due to the expansion of the universe stretching the signal. For their groundbreaking work, Penzias and Wilson won the Nobel Prize.