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10 Biggest Telescopes on Earth: How They Measure Up

Ten Huge Telescopes on Earth

ESO/L. Calçada

Next-generation ground telescopes received priority designation from a long-awaited report by the National Academy of Sciences. They would join a host of existing ground telescopes and smaller space telescopes already peering at supernovas, galaxies and other distant objects in the starry skies.

Three planned optical telescopes in the 98-foot (30-meter) range would house some of the biggest mirrors yet for collecting light from distant cosmic objects. And proposed radio telescope would dwarf predecessors by using many antenna stations to create a total collecting area of a square kilometer, or 0.4 square miles.

Here's a look at ten of the present and future giants among ground-based telescopes that provide scientists a glimpse of the past universe through time and space.

Related: Best Telescopes Guide 

Large Synoptic Survey Telescope (LSST)


A new ground-based observatory that would scan the entire available sky every three nights from Chile could see first light by 2014. The $465-million Large Synoptic Survey Telescope would give astronomers their best view ever of how billions of faint starry-sky objects change over time. It could also tackle questions relating to the nature of dark energy, and perhaps track space rocks that might collide with Earth in the future.

The optical telescope would image each region of the sky 1,000 times over 10 years with an almost 28-foot (8.4-meter) aperture. It represented a top priority among ground projects slated for the next 10 years in the Astro2010 Decadal Survey by the National Academy of Sciences.

South African Large Telescope (SALT)

SALT/Southern African Large Telescope consortium

This 30-foot (9.2-meter) telescope represents the largest ground-based optical instrument in the southern hemisphere, and concentrates on spectroscopic surveys. A main mirror consists of 91 hexagonal mirrors that join together to form the larger hexagonal primary —not unlike the Hobby-Eberly Telescope (HET) in Fort Davis, Texas.

Like HET, SALT also has a fixed-angle design that has complicated observations since it began operation in 2005. But the instrument can still view about 70 percent of the sky observable from Sutherland, South Africa.

Keck I and II Telescopes

The twin 33-foot (10-meter) telescopes at the W. M. Keck Observatory represent the second largest optical telescopes on Earth, located close to the summit of Hawaii's Mauna Kea. Each instrument's main mirror consists of 36 hexagonal segments that work together.

Keck I became operational in 1993, followed just a few years later by Keck II in 1996. The combined observatory has helped astronomers examine events such as last year's impact on Jupiter. It also deployed the first laser guide star adaptive optics system on a large telescope in 2004, which creates an artificial star spot as a reference point to correct for atmospheric distortions when viewing the sky.

Gran Telescopio Canarias (GTC)

Gran Telescopio CANARIAS (GTC)

A 34-foot (10.4-meter) telescope located on La Palma of Spain's Canary Islands seized the top spot as the world's biggest ground-based optical telescope in 2009. A main mirror that consists of 36 hexagonal segments contains some of the smoothest surfaces ever made.

The telescope also has several support instruments such as CanariCam, a camera capable of examining mid-range infrared light emitted by stars and planets. The CanariCam also has the unique ability to figure out the direction of polarized light and use coronagraphy to block out bright starlight and make fainter planets more visible.

Arecibo Observatory

NAIC - Arecibo Observatory, a facility of the NSF

One of the world's most recognizable ground-based telescopes has resided as a huge 1000-foot (305-meter) radio reflector dish near Arecibo, Puerto Rico since 1963. The Arecibo radio telescope still represents the largest single-aperture telescope ever constructed, with its spherical reflector consisting of 40,000 aluminum panels each 3 feet by 6 feet.

The huge reflector helps make Arecibo an incredibly sensitive radio telescope, capable of homing in on a faint radio source within just several minutes of observation. Such radio sources include distant quasars and galaxies that emit radio waves which only reach Earth 100 million years later.

Atacama Large Millimeter/submillimeter Array (ALMA)


One of the largest ground-based astronomy tools comes in the form of the 39-foot (12-meter) radio antennas that will total 66 by 2012, to make up ALMA's main array. Each antenna weighs more than 100 tons each and requires huge crawler vehicles to move it to Chile's Chajnantor plain at an altitude 3 miles up. This will ultimately help make ALMA the largest and most sensitive radio telescope ever, at least until a new contender emerges.

The antenna array can also undergo different configurations by moving individual antennas around. A compact configuration would place all the antennas within an area less than 1,000 feet across, or within an extended configuration with a maximum distance of separation between the antennas of almost 10 miles. This will allow the array to study everything from the cosmic "dark ages" billions of years ago to the processes of star and planet formation.

Giant Magellan Telescope (GMT)

Giant Magellan Telescope Observatory

One of the next ground-based optical telescopes will take the form of the $1.1-billion Giant Magellan Telescope with an 80-foot (24.5-meter) main mirror that consists of seven segments. One 8.4-meter segment would sit in the middle, surrounded by the other six segments that have a unique curved shape not unlike that of a potato chip.

The large main mirror would dwarf the current generation of 26 to 33-foot (8 to 10-meter) telescopes and produce images about 10 times sharper than the Hubble Space Telescope. If fully funded, the telescope could find a home at the Las Campanas Observatory in La Serena, Chile and begin full operations by 2024.

Thirty Meter Telescope (TMT)

Thirty Meter Telescope

Another of the next-gen contenders for biggest optical telescope on Earth is the Thirty Meter Telescope. The $1.4-billion telescope's 98-foot (30-meter) aperture would allow for more than 9 times the collecting area of the largest optical telescopes such as the Keck Telescopes, and could provide 12 times sharper resolution than the Hubble Space Telescope.

But TMT and other extremely large optical telescopes would not replace space telescopes. Hubble's successor, NASA's James Webb Space Telescope, would find targets for Earth-based giants such as TMT to study in more detail. The Thirty Meter Telescope is slated to join the Keck Telescopes and other instruments on Mauna Kea in Hawaii and commence full operations by 2025-2030.

Square Kilometer Array (SKA)

SPDO/TDP/DRAO/Swinburne Astronomy Productions.

A follow-up to radio telescopes such as ALMA is a telescope capable of collecting data over one square kilometer. The aptly-named Square Kilometer Array would become the clear king of radio telescopes, with 50 times the sensitivity of any radio telescope ever built. Such power could examine signals from the younger universe of 12 billion years ago.

Current plans call for either 30 stations with a collecting area of 656 feet (200 meters) each, or 150 stations each equivalent to a 295-foot (90-meter) telescope. South Africa and Australia have already begun jostling in a bid to play host to the $2 billion behemoth, scheduled for completion around 2020. It co-ranked as the highest priority project in the European Astronet Decadal Survey, along with the European Extremely Large Telescope.

European Extremely Large Telescope (E-ELT)


No ground-based optical telescope contender can currently match the design proposal for the European Extremely Large Telescope. Its 138-foot (42-meter) mirror would put it easily beyond the Thirty Meter Telescope and Giant Magellan Telescope, with a length reaching almost half a soccer field. Five mirrors consisting of almost 1,000 hexagonal segments would make up the primary mirror, and give Earth-bound astronomers the sharpest view ever of the cosmos in the visual-light spectrum.

Cerro Armazones in Chile will be the future home of the world's largest optical telescope. The $1.3-billion E-ELT would see first light around the same time as its smaller next-gen cousins in 2018.

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Jeremy Hsu

Jeremy Hsu is science writer based in New York City whose work has appeared in Scientific American, Discovery Magazine, Backchannel, and IEEE Spectrum, among others. He joined the and Live Science teams in 2010 as a Senior Writer and is currently the Editor-in-Chief of Indicate Media.  Jeremy studied history and sociology of science at the University of Pennsylvania, and earned a master's degree in journalism from the NYU Science, Health and Environmental Reporting Program. You can find Jeremy's latest project on Twitter (opens in new tab)