Largest optical telescope in the world

Modern cathedrals

Like the cathedrals, large telescopes can discover the composition of deep sky in visible and invisible light, the heavens are their domain. The analogy is bold, but modern cathedrals are giant telescopes because these prestigious buildings, large wingspans, are designed to reflect on the origin of our creation, the Big Bang.
However, the largest telescopes is to come, it will be located in the Atacama Desert in Chile, near the VLT and its first rays are planned for 2024-2026, it is called E-ELT (European Extremely Large Telescope). It is a modular giant, its main mirror measuring 39 meters in reality it is a mirror composed of 798 hexagonal segments (small mirrors of about 1.40 m wide and 5 cm thick), spread over a collecting surface of 1116 m².
This pharaonic instrument whose dome is ≈ 80 m in height, will be four to five times larger than the current VLT telescopes (image opposite) and collect about fifteen times more light. In addition to the primary mirror 39 meters in diameter, it will be equipped with a secondary mirror 4.2 m, two mirrors of 3.8 m and 2.4 m and an elliptical mirror 2.6 x 2 1 m.

Image: The VLT telescope, is a huge telescope, the flagship facility of European astronomy, built in the late twentieth century. It is a remarkable building both for its beauty, its design and its mirrors as for its installation site.

Image: St. Stephen's Cathedral Bourges is a huge cathedral built between the late twelfth and the end of the thirteenth century. It is a remarkable building both for its beauty, its design and stained glass windows for its installation site.

The largest optical telescope in the world

Giant telescopes due to their large opening used to collect light, lots of light to obtain remote images, ever finer. What do you want to do with giant telescopes?
Meeting the greatest scientific challenges of our time, in other words:
- see the birth of the universe, the Big Bang that took place there 13.7 billion years. See the first light of the birth of the so-called ordinary matter, the one we are done and especially the matter of which we are not done, dark matter and dark energy.
- see hidden aliens in this vast universe, i.e. see extrasolar planets of the mass of Earth, orbiting in the "habitable zone" of other stars.
- test our physical constants and our physical laws until Planck scale.
No doubt that this high technology monster also show us unexpected aspects of the universe, which will raise new questions, as always in cosmology when you jump over a conceptual cape.
To do this, scientists have invented in the 1990s, a revolutionary concept in optical machine, it is this concept that will be used to a wide scale in the 2020s with the E-ELT (European Extremely Large Telescope).
The technological revolution comes from the size of its instruments and in particular its segmented active optics system which allows to make giant mirrors. Indeed the size of the largest monolithic mirrors before ELT concept did not exceed 8.4 m, because beyond, industrial faced an insurmountable technical challenges. Solid primary mirrors of one piece of more than 8 m, does not support their own weight without deforming under the effect of gravity. In addition, the fragility and weight of the mirror no longer allowed its transport. The largest monolithic mirror (8.4 m), is the Subaru Telescope put into service in 1998 on Mauna Kea in Hawaii Site.
E-ELT has a giant primary mirror 39 meters in diameter. It consists of 798 hexagonal segments, 1.4 m wide and 5 cm thick, its collecting area is 978 m2, its total mass is about 150 tons. With this mirror the ESO telescope can cover a celestial field ≈5 ° (ten times the size of the full Moon). But for proper operation, all of the instrumentation require other mirrors. E-ELT is also equipped with a secondary mirror 4.2 m on which the light is reflected from the primary mirror.

The adaptive optics system consists of another large deformable mirror 2.4 m in diameter that corrects in real time, every millisecond, blurring images caused by the unpredictable atmospheric turbulence. This mirror is controlled by a computer that analyzes the vagaries of the atmosphere and distorts the mirror constantly acting on 7000 actuators (piezoelectric actuators i.e. electronic pistons placed on the other side of the mirror, which push or pull so that the total area preserves its ideal form).
To analyze the disturbances, the system needs a reference in the sky for this artificial stars are created using 5 to 6 lasers sodium. The Laser Guide Star (LGS) is used as a reference to correct the blurring effect of the atmosphere on images. The color of the laser is precisely tuned to energize a layer of sodium atoms present in one of the upper layers of the atmosphere. The laser beam bounces on this layer and brings up a reference star.
A multitude of other instruments will be created and tested on existing telescopes before being deployed in their giant version, the E-ELT.
The site chosen for this technological marvel is the Cerro Armazones mountain of 3064 m in the Cordillera de la Costa, located ≈130 km southeast of Antofagasta, Chile. Once the mountains leveled by diggers and excavators, giant telescope will be installed on the flat-topped ≈2800 meters.
Since December 2014, the telescope can enter the construction phase as the financial commitment has reached more than 90% of the total cost of the first phase.
"The funds already committed allow the construction of a fully operational E-ELT, which, thanks to a larger collecting area and its advanced instrumentation, will be the most powerful of the giant telescopes currently being designed. It will allow the initial characterization of Earth-type exoplanets, the study of stellar populations in nearby galaxies, as well as ultra-fine observations of the deep Universe, "concludes Tim de Zeeuw (Director General of ESO).

Image: Comparison of nominal dimensions of the primary mirror some notable optical telescopes. Mirrors are to scale and to get an idea of the size of each of these instruments, a tennis court, a basketball court and a man standing were added (bottom of the image). credit image: Wikimedia Commons

List of largest telescopes