A crescent Moon over the VLTI

Pictured here at sunset is one of the four Auxiliary Telescopes (ATs) of the Very Large Telescope Interferometer (VLTI), shown at ESO's Paranal Observatory. The faint crescent Moon can be seen hanging above the round enclosure of the telescope.

Together with four Unit Telescopes (UTs) that make up the Very Large Telescope, these four ATs complete the VLTI. Unlike the UTs, which are fixed, each of the four 1.8-metre ATs are movable and can be relocated to 30 different stations along the platform to create a wide baseline of up to 200 metres. This allows the VLTI to act as one large telescope of this size via a technique called interferometry — combining the light from several smaller telescopes to increase the resolution of the telescope. In the case of VLTI, this provides milliarcsecond angular resolution — equivalent to a span of two metres as far away from us as the Moon.

This image was taken by ESO Photo Ambassador, Gabriel Brammer.