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The Very Large Telescope – or VLT – has been responsible for some of the greatest astronomical breakthroughs of all time, discoveries that have resulted in Nobel Prizes and transformed our understanding of the cosmos. The Sky at Night team travels to the heart of Chile’s Atacama Desert to explore one of the most advanced observatories in the world - a site at the forefront of ground-based optical astronomy.

The Very Large Telescope, or VLT, is located at the Paranal Observatory, in the Atacama Desert, one of the driest places on earth apart from the North and South Poles, which makes it the perfect place for an observatory because there is little moisture in the air distorting the view of the stars.

The VLT is actually made up of four main telescopes that can be used individually or have their observing power combined. Each telescope contains a huge 8.2 metre mirror at its heart, designed to capture as much light as possible, and the images obtained from the ground are almost as sharp as those obtained in space.

In this episode, Maggie meets some of the scientists, engineers and astronomers working at this extraordinary site. Her journey begins by meeting the head of maintenance, support and engineering, Maxime Boccas. He is leading the operation of something that only happens once every two years – the cleaning of the mirrors. Maxime explains the incredible way these huge and delicate mirrors are cleaned and maintained – including the way aluminium particles are vaporised to create perfectly reflective surfaces.

Someone using the incredible telescopes for their work is astronomer Dr Joe Anderson. Along with other scientists, Joe uses the VLT’s specialised instruments – devices that analyse light from the universe, helping scientists to see and better understand the cosmos. Joe explains that the VLT is the world's most advanced visible-light astronomical observatory, and its huge mirrors and range of instruments mean astronomers can get readings across a broad range of spectrums, which has led to a lot of new discoveries regarding exoplanets, black holes and gamma ray bursts.

The VLT is a huge site in the middle of a desert, so Maggie next meets Vanessa Peidro, the head of logistics and responsible for maintaining not just the buildings and vehicles but also managing food, water and other facilities that cater for 150-160 people on site at any one time.

Maggie then meets physicist Francoise Delplancke-Stroebele and her colleague Frederic Gonte. They are leading the VLT's next upgrade, Gravity+, and explain how the four massive telescopes at the VLT work in unison by combining light waves in a technique called interferometry. This technique is used by astronomer Dr Abigail Frost, who explains how interferometry helped in the recent discovery of a rare so-called ‘vampire star’.

The VLT is still a world-class observatory with cutting-edge research, but the site will soon transform into an even more powerful observatory. The Extremely Large Telescope, or ELT, is currently in construction. Maggie gets a sneak peek at what will be, when it’s completed in five years’ time, the biggest optical telescope in the world. Built on top of a mountain and the size of a cathedral, the ELT has to be one of the most spectacular and complex feats of engineering in the world.