The E-ELT in numbers

• Main mirror diameter: 39 metres
• Light collecting area: 978 square metres

39-metre diameter

With its main mirror as large as 39 metres in diameter, this will be the largest telescope to observe in visible-light. It will be four to five times larger than the present-day state-of-the-art facilities of this kind, and will collect about 15 times more light. It will also be much larger than the two other extremely large telescopes in planning, the Thirty-Meter Telescope and the Giant Magellan Telescope.

Almost 800 segments

It is not possible to build such a large mirror in one piece. Instead, the 39-metre diameter primary mirror will be composed of 798 hexagonal segments, about 1.4 metre wide and 5 cm thick. The whole concept of the telescope is to be modular, so that pieces can be manufactured in large quantities, thereby drastically reducing the cost. Only this approach makes the E-ELT possible within a restricted budget.

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