VLT Telescopes at sunset

The Sun is setting, and the sky is cloudless. A great night for astronomical observations is coming at the Paranal Observatory, where ESO’s Very Large Telescope (VLT) is located. The VLT consists of four Unit Telescopes (UTs) and four movable Auxiliary Telescopes. The four Unit Telescopes, with a main mirror of 8.2 metres, are hosted in compact and thermally controlled buildings, which move simultaneously with the telescopes. These containers are more than 28 metres high, and almost 30 metres in diameter. From right to left, the Unit Telescopes are UT1, UT2, UT3 and UT4. These four telescopes are mostly used for individual observations, but they can also work together as a giant instrument, dubbed ESO Very Large Telescope Interferometer. On the left, the smaller domes are three of the 1.8-metre Auxiliary Telescopes, which feed the light to the VLT Interferometer. They can be moved to 30 different positions, and each telescope is housed in a casing more than six metres high, and almost four metres in diameter.