Radio telescopes increase their aperture primarily by using larger dish or antenna sizes. The aperture of a telescope is essentially the diameter of its collecting area, which directly affects its sensitivity to low-radio signals. Larger apertures collect more radiation and can detect weaker signals, allowing astronomers to observe distant and faint celestial objects with greater clarity. Radio telescopes achieve larger apertures by building larger antenna dishes or arrays.
For example, the Arecibo Observatory in Puerto Rico had a massive dish spanning 305 meters in diameter, making it one of the most sensitive radio telescopes in the world until its collapse in 2020.
Radio telescopes need large apertures to gather sufficient amounts of radio waves from extremely faint sources in space. Unlike visible light, radio waves from cosmic sources are often very weak by the time they reach Earth due to their long journey through space and interactions with interstellar materials.
A larger aperture allows a telescope to collect more photons and therefore increase its signal-to-noise ratio, allowing astronomers to detect and study fainter objects and phenomena. Large apertures also improve the telescope’s angular resolution, allowing it to distinguish fine details in distant objects.
The resolving power of a radio telescope, or its ability to distinguish fine details in the sky, can be increased by several methods.
One approach is to increase the physical size of the telescope aperture, because larger apertures provide better resolution due to their ability to capture finer spatial detail in radio images. Another method is to use interferometry, where several smaller telescopes or antennas are combined to simulate a larger virtual aperture.
Interferometry allows radio telescopes to achieve extremely high resolution by synthesizing signals from widely spaced antennas, effectively creating a telescope with an aperture as large as the maximum separation between the antennas.
Aperture synthesis is a technique used in radio astronomy to combine signals from multiple small telescopes or antennas spread over a large area to simulate a single, larger aperture. This method effectively creates a virtual telescope with the resolving power of a much larger instrument.
By combining signals from widely spaced antennas using precise timing and data processing techniques, aperture synthesis allows radio telescopes to achieve very high angular resolution. This capability allows astronomers to study fine details in radio sources with unprecedented clarity, revealing structures and dynamics otherwise invisible to single-channel telescopes.
Radio telescopes can indeed “see” further into the universe compared to optical telescopes in some respects.
While optical telescopes observe visible light, which can be absorbed or scattered by cosmic dust and gas, radio waves can penetrate these obstacles more effectively. Additionally, radio waves emitted by some astronomical sources, such as neutral hydrogen gas in distant galaxies, can travel great distances through space without significant attenuation. This allows radio telescopes to detect and study objects that may be obscured or invisible in optical wavelengths, providing unique information about the structure, composition and evolution of the universe across vast cosmic distances