The 10 biggest telescopes on Earth

1. The Gran Telescopio Canarias (the Canaries Great Telescope) – GranTeCan or GTC.

The GTC is currently the largest optical telescope in the world. Here, the word “largest” refers to the size of the lens with which the telescope captures light. A larger lens or what is today called a mirror in professional telescopes captures more light and enables the observation of smaller objects. The GranTeCan mirror measures 34 ft (10.4 m) in diameter and is composed of 36 hexagonal segments. It is located 7438 ft (2267 m) above sea level at the Roque de los Muchachos Observatory on La Palma in the Canary Islands.


Photo: Pablo Bonet.

2. The twin telescopes Keck I in Keck II capture light with two 33-feet (10-metre) segmented mirrors.

Keck I and Keck II are located 13,796 ft (4,145 m) above sea level atop Mauna Kea, a dormant volcano in Hawaii. The telescopes have an adaptive optics system that uses an artificial star, created in the Earth’s atmosphere using a laser, to correct the images that are blurred due to atmospheric interference.


Photo via Wikimedia.


“Keck laser at night” by Paul Hirst (Phirst) via Wikimedia.

3. The Very Large Telescope (VLT) is actually composed of four telescopes: Antu (or the Sun in the language of the Mapuche tribe), Kueyen (the Moon), Melipal (the Southern Cross) and Yepun (Venus as the evening star).

Their mirrors measure 27 ft (8.2 m) in diameter and are made of one piece. Although they are only 0.57 ft (17.5 cm) thick, they weigh 23 tons. The VLT is the pride of the European Southern Observatory (ESO) and stands at 8,645 ft (2,635 m) above sea level in the Chilean Atacama Desert, more precisely at the Paranal Observatory. In collaboration with a group of international astrophysicists, the VLT is also used by Slovene astronomers. Close by, on the mountain Cerro Armazones, the European Extremely Large Telescope (E-ELT) with a 128-feet (39-metre) mirror is expected to be built in the next few years.


Photo: ESO/Gabriel Brammer.


Photo: ESO/Iztok Bončina. For more photos click here.

4. The Large Binocular Telescope.

Standing at 10,586 ft (3,221 m) above sea level at the Mount Graham International Observatory in Arizona, USA, this telescope is composed of two 27.5-feet (8.4-metre) one-piece mirrors. The centre-to-centre spacing between the two mirrors is 47 ft (14.4 m), which enables the telescope to have the same angular resolution (image sharpness) as a mirror that measures 75-feet (22.8-metre) in diameter.


“LargeBinoTelescope NASA” by NASA (Transferred by Quantanew/Original uploaded by Mohamed Osama Al Nagdy). Photo via Wikimedia.

5. The Atacama Large Millimetre/Submillimetre Array (ALMA).

The ALMA comprises 66 antennas which are spread over an area of 6 square miles (16 sq km) on the Chajnantor plateau in the Chilean Andes. These antennas capture light with a wavelength of around a millimetre, which is somewhere between infrared light and radio waves. This light comes from the very cold interstellar gas clouds where stars are born, and from some of the most distant and earliest galaxies in the Universe. The antennas can function together as an interferometer to achieve exceptional angular resolution (image sharpness).


Photo: Iztok Bončina/ALMA.


Photo: ESO/C. Malin.

6. The Low-Frequency Array (LOFAR) is currently the largest radio telescope.

It is composed of 25,000 small antennas which are assembled in 48 large stations. Forty of these stations are located in the Netherlands, five in Germany and one of each in the UK, France and Sweden. The total effective collection area is around 300,000 square metres.


Photo: Top-Foto, Assen.

7. The MAGIC Telescopes are located on the Roque de los Muchachos Observatory on La Palma in the Canary Islands and are called the Cherenkov telescopes.

The high-energy photons of gamma rays do not pass through the Earth’s atmosphere to the surface, but collide with air molecules, producing a shower of elementary particles. The particles moving through the air faster than the speed of light emit a faint Cherenkov radiation observed by the two 56-feet (17-metre) telescopes. This makes it possible on Earth to indirectly observe the gamma radiation generated by “wild” astronomical processes, such as objects falling into black holes in the centres of galaxies, supernova remnants and X-ray binary stars. The results of the MAGIC, HESS and VERITAS projects will be used for a large international project, the Cherenkov Telescope Array (CTA), which also involves the University of Nova Gorica.

Information on what is happening in space is gathered not only from light of different wavelengths, but also from cosmic particles, neutrinos and gravitational waves. Systems for their detection are visually very different from “regular” optical telescopes, but since they enable the “observation” of events in outer space they are classified as astrophysical observatories (they are part of “multi-messenger astronomy”).


Photo via Wikipedia.

8. Cosmic particles are high-energy particles whose exact origin has not yet been fully established. In most cases (99%), they are actually atomic nuclei (around 90% are hydrogen nuclei or protons, 9% helium nuclei and 1% heavier atomic nuclei). The remaining 1% is composed of electrons and in a very small proportion also of antiparticles – positrons and antiprotons. When entering the Earth’s atmosphere, cosmic particles collide with air molecules and cause a shower of secondary elementary particles that sometimes reach the Earth’s surface. The largest observatory for detecting these showers and cosmic particles is the Pierre Auger Observatory in Argentina, whose several detectors are located in an area of 1,158 square miles square feet (3,000 square kilometres) in the Pampas region. This year, the observatory is going to be upgraded. The Pierre Auger Project also involves Slovene scientists from the University of Nova Gorica.


9. Neutrinos are elementary particles created in large numbers during many processes in the universe (nuclear reactions in the Sun, supernova explosions, etc.). As they barely interact with matter, they pass practically uninterruptedly through everything. That is why detecting them presents such a difficult challenge. The common denominator for all detectors of space neutrinos is a large quantity of matter where neutrinos are expected to leave a trace: in large underground water and seawater reservoirs and in the Antarctic ice used in the IceCube experiment. The IceCube detector is composed of thousands of sensors at a depth of 5,000–8,000 ft (1500–2500 m) beneath the ice’s surface, through a volume of one cubic kilometre.

ice cube

“Icecube architecture – diagram 2009” by Nasa-verve – IceCube Science Team – Francis Halzen, Department of Physics, University of Wisconsin. Via Wikimedia.

ice cube

Photo: Felipe Pedreros. IceCube/NSF.

ice cube

Photo: IceCube/NSF.

10. Gravitational waves were predicted by Einstein’s general theory of relativity. They are created when objects with mass move around in a certain space; for example, they are thought to be created by a collision of two massive neutron stars or black holes. Their existence was indirectly proven in the binary pulsar system, while direct detection is technically extremely demanding. The most sensitive experiment for their detection is the American Laser Interferometer Gravitational-Wave Observatory (LIGO). It has two interferometer observatories, each having a 13,123 feet (4 kilometres) long system with an ultra-high vacuum.


(Note: Such lists are always, at least to some extent, subjective. And this is my list.)


Author: Andreja Gomboc, astrophysicist. Researches the most powerful explosions in the universe and lectures on astronomy and astrophysics at the Faculty of Mathematics and Physics in Ljubljana. Since she wants to propagate curiosity and knowledge about outer space, in her spare time she runs a Slovene website called the Portal to the Universe.


Translated by: Sarah Humar.


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