On the VLT platform at night

The first of the four VLT 8.2-metre Unit Telescopes (UTs), called UT1 or Antu, during observations. In front of it is the second of the four 1.8-metre Auxiliary Telescopes, the AT2. Each UT is housed in a compact building which rotates synchronously with the telescope. In this long exposure, the rotation of the building can be appreciated. The ATs always work in pairs or in a group of three, using a technique called interferometry, which allows astronomers to see details up to 25 times finer than with the individual telescopes. The configuration of the ATs can be changed across the platform by moving them to 30 different observing positions. One of these positions, covered by a hexagonal pad is visible in the picture.