VLT telescope. Astronomer Jason Spyromilio tests part of the azimuthal mount of telescope UT 1 at the Very Large Telescope (VLT). The VLT is based at the European Southern Observatory site at Cerro Paranal, Chile. The VLT consists of four such telescopes in separate buildings, this one being the first to become operational in May 1998. The azimuthal mount can rotate vertically and horizontally, and carries an 8.2-metre diameter mirror. All four VLT telescopes, when used together, will have the light-collecting power of a 16-metre mirror, making the VLT the world's largest optical telescope. The VLT is due to be completed soon after 2000.