OPTICAL telescopes have come a long way since Sir Isaac Newton decided it was better to use mirrors instead of lenses for astronomy 347 years ago.
Going from the 33mm mirror mounted on a wooden ball in Newton's office to the upcoming 6.5m James Webb telescope sitting at the L2 Lagrange point near Earth has been a process involving some of the most important developments in technology and science.
Even though these enormous telescopes exist, there is still so much to learn, see, and discover simply by being outside in the right weather with a telescope you can carry under your arm.
Maybe one day you'll be making observations through a space-based telescope sitting in a Lagrange point.
Meanwhile, you can score a telescope in our Amazing Space competition
In the meantime, here are the five largest optical telescopes on Earth and the amazing things they're capable of.
Number 5: The Large Binocular Telescope (LBT)
Effective Aperture: 8.4m (x2)
The LBT is proof of how technically clever physicists and engineers have become. Instead of building one large, costly and daunting mirror, the minds behind the LBT decided to build two 8.4m mirrors working together as binoculars.
Splitting the so-called 'collecting area' over two offset mirrors allows the LBT to gather as much light as an 11.8m mirror and to capture the same detail as a 22.8m mirror.
The secondary mirror setup has been designed to correct for the distortion the atmosphere causes in the images the observatory takes. The sophistication of these 'adaptive optics' means that the LBT can match and sometimes beat even the Hubble Space Telescope for sharpness on certain wavelengths.
The LBT has been used for everything from investigating lava on Jupiter's moon Io to discovering a black hole with the "mass of 12 billion solar masses and the luminosity of 420 trillion solar luminosity, at a distance of 12.8 billion light-years from the earth."
Number 4: Hobby-Eberly Telescope (HET)
Effective Aperture: 9.2m
The engineers behind the HET chose a different method for beating the difficulties of creating such enormous mirrors. Instead of one large and expensive 9.2m mirror, this telescope uses 91 hexagonal mirrors placed together with extreme precision.
The HET's design departs from the orthodox in a few ways, including the mirror's paraboloid shape, fixed angle and versatility, but its achievements are fascinating even as far as giant telescopes go.
The mirrors in the HET are so finely tuned they're able to measure the radial velocity of distant stars with a precision of up to 1m/s - allowing it to discover and observe planets orbiting those stars. There's a good shot that this telescope will be in the history books when it comes to writing the chapters on life in the universe.
One of the more 'fun' projects the HET has been involved in lately has been measuring the mass of a black hole approximately 17 billion times more massive than our sun. So far, this is the largest black hole we've measured, and current estimates put it at 59% of the total mass of its host galaxy.
Number 3: South African Large Telescope (SALT)
Effective Aperture: 9.8m
SALT is the largest telescope in the southern hemisphere, sitting 1,798m above the Sutherland region in a national park in South Africa.
Like the HET, the way SALT was built came down to minimising the extreme cost of building a 10m-class telescope. The primary mirror uses 91 hexagonal mirror segments (though this time in a slightly larger spherical configuration) and instead of being placed in a fully manoeuvrable mount, the telescope is limited to simply rotating while more precise angling is taken care of by a 'payload' at the primary focus point. This means that the telescope is simpler and cheaper but can't focus on a single target for long periods.
SALT is significant in its differences from other large telescopes of its class. Not only is it able to observe the southern hemisphere more effectively than its counterparts, it is also optimised for seeing different wavelengths of light.
So far, SALT's optical trickery and size has led to the discovery of a new type of star system and huge improvements in our measurements of type 1a supernovae - the explosions we used to calculate by how much the expansion of the universe is speeding up.
Number 2: W. M. Keck Observatory (Keck)
Effective Aperture: 10m
The Keck 1 and 2 telescopes are not only the second largest observatories on Earth, they're also located in what's currently considered the best place to sit a giant telescope - the summit of Mauna Kea in Hawaii.
Keck 1 and 2 popularised the use of hexagonal mirror segments instead of one giant primary mirror, the same systems used for the HET and SALT. It's also possible for the two to be used in a similar 'binocular' configuration as the smaller LBT, turning the two telescopes into an 85m optical interferometer.
Each of the Keck telescopes weighs more than 300 tonnes.
The sheer amount of technology and engineering involved with the Keck Observatory one of the most scientifically productive observatories available.
Number 1: Gran Telescopio Canarias (GTC)
Effective Aperture: 10.4m
The GTC is the largest optical telescope on earth and one of the newest and most sophisticated of the batch.
The GTC's primary mirror alone weighs 17 tonnes while the total telescope moving weight is 400 tonnes. To put this in perspective, imagine trying to aim 230 Holden Commodores to point at a target the size of 2 DVDs 24 kilometres away.
The description provided by the GTC website is so wonderfully bonkers that it bears repeating:
To get an idea of the vast GTC observation capabilities, we can compare its power of vision to 4 million human eyes and, with it, we could distinguish car headlights some 20,000 km away, or at the distance that separates Spain from Australia.
Astronomers at the GTC caught first light with the massive telescope in 2007 and saw an accelerated growth in the number of peer-reviewed papers published from its observations, hitting the 100 papers published well within the first five years of operation.
With the observational power of the GTC, we've been able to learn some of the inner secrets of how objects in our solar system are formed and behave. One of the most useful of these lessons is the internal structure of main belt objects - the giant rocks mega-corporations around the world are planning on mining in the near future.
Like SALT, GTC has also been making key discoveries in the search for earth-like exoplanets, with several discoveries including finding elements required for life.
The giants on the horizon
The GTC will be the last of the 10m-class ground observatories built as organisations across the world move to giants like the 42m European Extremely Large Telescope (ELT).
Extremely large telescopes aim to hit the next big benchmarks in optical astronomy, which are mainly involved with the hunt for exoplanets and seeing back to the very first galaxies.
The best telescope on Earth: Yours
Effective aperture: your call
Few of us will ever have the opportunity to use the LBT or GTC (prove me wrong!), so in the end, the best telescope in the world is the one you get to look through yourself.
No descriptions or photos on the internet can compare to seeing the cosmos for yourself, so why not check out an astronomy club and see if you can have a peek through someone's telescope. Maybe you'll fall in love and grab your own.
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