In graphics: Large Binocular Telescope

Consisting of two perfect 8.4m mirrors, the instrument will be used to look for extrasolar planets, probe the massive black holes at the centres of galaxies and look at objects forming a few hundred million years after the Big Bang.

The LBT has been designed to offer astronomers as much flexibility as possible. The two large mirrors can be used separately with different instruments above each. These are swung into position on gantries and allow different aspects of the same object to be measured simultaneously.

LBT INSTRUMENTS

• Large Binocular Cameras above each mirror take images in the infrared and ultraviolet
• PEPSI spectrograph will be used to understand the magnetic fields of stars
• MODS consists of two optical spectrographs to analyse distant objects
• LUCIFER consists of two infrared spectrographs able to image multiple objects at once
• AGW units will help track objects and correct for atmospheric distortion
• LINC-Nirvana produces wide-field, high-resolution images
• LBT interferometer allows detection of nearby planets obscured by bright stars

Telescope's double vision

However, the light from each mirror can also be combined to make one high-resolution image. Here is how it works:

1. As the light enters the telescope and hits the huge mirrors - the largest ever made from a single piece of glass - it is deflected towards the secondary mirrors above.

2. Because the Earth's atmosphere distorts the light from stars, adaptive optics are used to correct the image. Moving magnets on the back of the secondary mirrors can change their shapes 1,000 times second.

3. The corrected light is deflected towards the centre of the telescope where one of various instruments combines the beams.

4. The dynamic balancing system compensates for movements of the telescope and helps it remain fixed on one spot in space.

5. The light can be used in different ways. The LBT interferometer (LBTI) can be used to reverse its phase, effectively cancelling the light from a bright star and allowing astronomers to look for faint, orbiting planets.

6. The interferometric camera is used to combine the light in phase, allowing high-resolution images to be taken. In this mode, the telescope has the equivalent sharpness of a 22.8m (75ft) instrument.