Teamwork makes an astronomer’s dream work

Why use just one telescope to observe the sky? The plateau of Cerro Paranal, seen under the moonlight in this Picture of the Week, hosts ESO’s Very Large Telescope Interferometer (VLTI), an indomitable team of four 8.2-metre Unit Telescopes (UTs) and four additional 1.8-metre Auxiliary Telescopes (ATs). 

An interferometer precisely combines light from separate telescopes observing the same object in the sky, allowing astronomers to see the cosmos in incredible detail. The VLTI uses either a combination of the ATs or the UTs. The ATs, one of which is seen front and centre, are set on tracks so they can be moved to 30 predefined positions on the platform, in different configurations; each arrangement allows astronomers to observe different levels of detail.

While the ATs are specifically designed for the VLTI, each UT can be also used as an independent telescope. One of the UTs is equipped with lasers that allow astronomers to get very crisp images through a process called adaptive optics. The lasers, powerful beams of light, excite sodium atoms in the atmosphere 90 kilometres above the ground, creating artificial stars that the telescope can use to measure how the atmosphere distorts the light from objects in the cosmos. Soon, the other three UTs will have laser guide stars of their own, allowing the VLTI itself to harness this unique power.