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4 of the World’s Largest Telescopes

At one time or another most of us have gazed into the night sky through the lens of a cheap telescope. 

Since the beginning of time everyone from Native Americans and Mesopotamians to Mayans and the builders of Stonehenge have left records of their astronomical observations. 

Though stargazing has always been a popular human endeavor, it wasn’t until the early years of the 17th century that actual telescopes began showing up in European workshops and observatories.

Galileo Galilei often gets credited with its invention, but the first telescope was built by Dutch tinkerer, glass maker and amateur astronomer Hans Lippershey.

Telescopes use lenses, curved mirrors and other devices to observe far away objects – often with surprising clarity. 

In years past they were used for both earthly and heavenly applications, but they were crude, delicate, and woefully underpowered.  

Now a new breed of telescopes uses everything from infrared sensors, radio waves, and massive composite mirrors to peer into corners of the cosmos that pioneers like Nicolas Copernicus, Johannes Kepler and Edwin Hubble could’ve scarcely imagined. 

And many, like the ones on this list, are downright epic in proportions. 


World’s Largest Telescopes in china (FAST telescope)
FAST Telescope by Absolute Cosmos is licensed under CC-BY

As of 2016 the world’s largest radio telescope, China’s Five hundred meter Aperture Spherical Radio Telescope, or FAST, was officially up and running.

Nestled inside a natural indentation in remote Guizhou Province – a place more well-known for rural villages, majestic mountains and stunning waterfalls – the massive listening telescope is often referred to as Tianyan, or “Eye of Heaven,” though “Ear of Heaven” may be more appropriate.

FAST is operated by the Chinese National Astronomical Observatory, and some estimates suggest that the project cost nearly $200 million.

Though its price tag was staggering enough, the government apparently spent at least that much modernizing the traditionally poor and agricultural area around the telescope to include a museum, a vineyard, hotels, and trendy restaurants featuring high-end Chinese and international cuisines that should help attract tourists with fat wallets from far and wide. 

There’s no denying that FAST is the largest telescope of its kind in the world, but its name is a bit misleading, because although its diameter is 500 meters (1,640 feet), only about 60% of its surface area is usable at any time. 

In that respect it’s much like the previous record holder for largest radio telescope, the one found at the Arecibo Observatory in Puerto Rico, another parabolic dish with a diameter of just over 300 meters, or 1,000 feet. 

But unlike Arecibo, FAST features a much deeper dish that gives it a wider field of view, and it’s not just larger, but more advanced and flexible as well. 

While the telescopic dish at Arecibo is fixed, FAST’s operators can distort its shape by using more than 2,000 individual winches positioned to the steel structure underneath that are capable of manipulating the 4,500 panels that make up its surface, thereby allowing it to focus on different parts of the sky with relative ease. 

In other words, FAST is a huge step forward for radio astronomy. 

FAST’s goals include observing pulsars with 50 times more accuracy than predecessors, detecting interstellar molecules, and continuously monitoring for extraterrestrial communications from the far reaches of space. 

It’s also scheduled to perform two comprehensive sky surveys which will take about 5 years, after which the data collected will likely need to be studied and analyzed for another decade before unlocking its true worth. 

With FAST, researchers will also be able to measure extremely low-frequency gravitational waves for the first time.

According to the Xinhua, China’s official state-run news agency, FAST’s performance has either met or exceeded expectations on every level, and early successes include the discovery of more 100 new pulsars in just a few years, more than its American and European counterparts combined during the same time period. 

So far, China has allowed a number of astronomers and researchers from other countries to visit the facility and work alongside its own scientists, though it’s rumored that staffing has been a challenge due to the country’s shortage of trained radio astronomers and the area’s remoteness. 

Gran Telescopio Canarias 

world's largest telescope Gran Telescopio Canarias
Gran Telescopio Canarias

Located nearly 7,500 feet (2,270 m) above sea level in the remote Canary Island of La Palma off the coast off northwest Africa, Gran Telescopio Canarias (GTC) may occupy some of the world’s best real estate for instruments built to observe the heavens. 

Though its roots date back to the late ‘80s, the Gran Telescopio Canarias (GTC) currently holds the top spot in a number of categories including the largest infra-red and single aperture telescope in the world.

The GTC was originally envisioned as a joint venture between Spain and the UK, but just a few years into planning Britain abandoned the project. 

Its future was bleak, but Spain pushed forward on its own, eventually bringing the much-anticipated telescope to fruition and becoming a global player in the astrophysics arena.

Despite including thousands of workers from hundreds of companies, construction dragged on much longer than expected due to technical glitches, harsh weather, and the region’s ruggedness and relative inaccessibility. 

Nonetheless, after 7 years and $150 million (€130 million) the telescope first opened its eye to the sky in mid-July of 2007, but it would be another 2+ years before teething issues were addressed and it became fully operational.  

With a primary mirror measuring 34 feet (10 m) across, a total moving weight of 400 tons, and an effective collecting area of nearly 80 mthe GTC isn’t only big, but it’s arguably the best performing astronomical research telescope in the world. 

But impressive specs aside, it’s how it sees into the cosmos that makes it a real standout. 

Its primary mirror is actually composed of three dozen individual hexagonal segments that act as a single reflecting unit. 

Back in 2016 the telescope captured images of a galaxy 500 million light years away – or by some estimates nearly 10 times farther into space than any other ground-based telescope was capable of peering at the time.

The telescope’s large mechanized steel superstructure allows it to move both horizontally and vertically and adjust with the precision necessary to keep the objects it’s viewing centered. 

The GTC also has secondary and tertiary mirrors that work in conjunction with the primary mirror to collect information that’s eventually fed to a host of instruments and computers that process, analyze and store it. 

The Spanish super-telescope is also well-known for the amazingly detailed images of galaxies, star clusters and black holes it’s captured from hundreds of millions of lightyears away.  

The Perseus galaxy cluster for example, though not particularly far from earth by space standards, contains nearly 200 individual galaxies, and is purported to be one of the universe’s largest objects.

In 2014, GTC astronomers detected strange emissions from unknown elements coming from Perseus, which they surmised were actually previously unseen particles of dark matter. 

The GTC is now a multinational partnership supported by the governments of Spain, Mexico, and the University of Florida in the United States, with member scientists being allotted time with the telescope in proportion to the percentage of funding their organizations provide.

Though it’s a marvel for now, the GTC is among the last of the 8 to 10 meter-class telescopes that’ll probably become obsolete in the not too distant future. 

Daniel K. Inouye Solar Telescope

world's largest telescope Daniel K. inouye Solar Telescope
Daniel K. inouye Solar Telescope by NSF/NSO/AURA is licensed under CC-BY

Naming a world-class astronomical observatory after a career politician with a past full of alleged ethics violations may leave a bad taste in some astronomers’ mouths, but that’s exactly what happened with the largest solar telescope in the world.

Though it was initially called the Advanced Technology Solar Telescope, The Daniel K. Inouye Solar Telescope (DKIST) was renamed after Hawaiian senator Daniel Inouye in 2013.

It all began nearly a decade ago the National Science Foundation awarded a $300 million contract to the Association of Universities for Research in Astronomy to build the facility on top of Maui’s Mount Haleakalā – a 10,000+ foot (3,060 m) behemoth looming over the idyllic island below. 

In traditional Hawaiian language Haleakalā means “House of the Sun,” which is an apt name considering the telescope’s main focus is studying our closest star neighbor. 

But the proposed site was opposed by locals who considered it sacred, and between 2015 and 2017 constant protests impeded construction vehicles from delivering supplies to the mountain’s peak. 

To the satisfaction of some however, issues were sufficiently addressed, and construction went ahead with the stipulation that the mountain would remain open to natives who wished to practice their religion there, albeit despite constant noise and deforestation. 

Featuring a moderate 13-foot (4 m) primary mirror, the DKIST may be little more than a coffee saucer compared to China’s FAST telescope, but it’s the largest, most capable, and most advanced solar telescope in the world. 

The DKIST’s dome was finished in 2016 and its primary mirror was delivered the following year, though it wasn’t until the end of 2019 that it began full-scale observations. 

Just a few months later in the beginning of 2020, telescope operators released amazingly detailed images of the sun that shocked laymen and the scientific community alike. 

It turns out that the sun’s surface resembles… drumroll please – corn.

More specifically, each kernel is represented by a solar convection cell roughly the size of Texas – America’s second largest state behind Alaska.

Perhaps more impressive is that for these high-res images, only the telescope’s Visible Broadband Imager was functional. 

A second key piece of equipment, the Visible Spectro-Polarimeter, designed to split sunlight into its component parts didn’t come online until later. 

Over it’s planned 5-decade lifespan, DKIST may solve some of the sun’s most enduring mysteries, like why it’s outer corona is much hotter than its visible surface, and how mass coronal ejections form. 

Far from being a static facility destined for obsolescence, DKIST’s upgradability and customizability may help it stay on the cutting edge for decades to come. 

In all, the telescope will witness the sun through at least 4 11-year cycles, and areas of future study include analyzing the solar atmosphere, infrared wavelengths, the sun’s magnetic fields, and identifying its component atoms and molecules. 

South African Large Telescope 

world's largest telescope South African Large Telescope 
South African Large Telescope by Lengau is licensed under CC-BY-SA

Often referred to as “Africa’s Giant Eye on the Universe,” South African Large Telescope – or SALT – is the largest single optical telescope in the southern hemisphere. 

And though the other telescopes on the list are all located in undeveloped areas with little by way of manmade light to interfere with their work, it’s claimed that SALT’s high-altitude South African location makes it the world’s darkest observatory.

SALT is part of the South African Astronomical Observatory field station near the Northern Cape Province town of Sutherland, about 250 miles (400 km) northeast of Cape Town, where it sits nearly 6,000 feet (1,800 m) above sea level.  

Though it’s primarily funded by the country’s National Research Foundation, other funding comes from universities and research institutes from all over the globe including the UK, India, Poland, New Zealand and America. 

Construction began more than two decades ago, but though initial observations were made five years later, the telescope’s full potential wouldn’t be realized until years later in 2011. 

Tipping the scales at nearly 90 tons and featuring a slightly oblong 30 x 36 foot (9 x 11 m) diameter mirror cluster with a 260 ft2 (80 m2) collection area mounted onto a 45 ton steel frame, the telescope’s primary mirror is actually composed of 91 smaller mirrors – each a fully adjustable 3-foot (1 m) hexagon made of low-expansion glass. 

The telescope is unique in that when it’s being used, the mirror remains at a fixed altitude and azimuth, and though the image it’s tracking is actually moving, it’s capable of following objects by way of a moving instrument package called a “payload” located about 40 feet (13 m) over the center of the mirror’s prime area of focus.  

To make all this work, the telescope relies heavily on a Center of Curvature Alignment Sensor housed in a tower adjacent to its retractable dome. 

When laser light is shone down on all the segments and the position of the reflections from each mirror is measured, a process known as “stacking” allows the operators to optimize each mirror’s adjustment, thereby ensuring complete coverage. 

As for impressive capabilities, it can collect more than 20 times as much light as any other African telescope, and detect modest light equivalent to that put off by a candle as far away as the moon, or about 239,000 miles (384,000 km) away. 

It was also credited with detecting the first white dwarf pulsar in 2016. 

Perhaps even more impressive however, was that when inflation was taken into account from the original late ‘90s cost projections, the project actually came in on budget. 

An almost unheard of accomplishment, especially considering it was a paltry $36 million USD to start with – about half of which was for construction, and the rest for instruments and operations. 

In addition, construction was carried out exclusively by South African companies, and more than half of the components were made in the country as well.

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