Auxiliary Telescopes

The four Auxiliary Telescopes (ATs) are 1.8m diameter telescopes that feed light to the Very Large Telescope Interferometer at ESO's Paranal Observatory. Uniquely for telescopes of this size they can be moved from place to place around the VLT platform and are self-contained. They were built by AMOS (Belgium). Further information here: eso0402.

The top part of each AT is a round enclosure, made from two sets of three segments, which open and close. Its job is to protect the delicate 1.8-metre telescope from the desert conditions. The enclosure is supported by the boxy transporter section, which also contains electronics cabinets, liquid cooling systems, air-conditioning units, power supplies, and more. During astronomical observations the enclosure and transporter are mechanically isolated from the telescope, to ensure that no vibrations compromise the data collected.

The transporter section runs on tracks, so the ATs can be moved to 30 different observing locations. As the VLT Interferometer (VLTI) acts rather like a single telescope as large as the group of telescopes combined, changing the positions of the ATs means that the VLTI can be adjusted according to the needs of the observing project.

Science goals

VLTI support

Live Images

Follow the Auxiliary Telescopes on these live images updated every hour during daytime. The telescopes can be relocated to many different stations to change their geometric configuration. The live images show some of the most used stations, but there might be no telescope there. Click on the thumbnails to enlarge.

A1 station LIVE. Here you may be able to see the AT1

K0 station LIVE. Here you may be able to see the AT3. On
extremely clear days the magnificent 6739-metre volcano
Llullaillaco is visible in the background of this photograph. It is
an amazing 190 kilometres away on the border with Argentina.


G1 station LIVE. Here you may be able to see the AT4



Auxiliary Telescopes

Name: Auxiliary Telescopes
Site: Cerro Paranal
Altitude: 2635 m
Enclosure: Relocatable dome
Type: Relocatable interferometric telescope
Optical design: Ritchey-Chrétien with Coudé optical train
Diameter. Primary M1: 1.82 m
Material. Primary M1: ZeroDur
Diameter. Secondary M2: 0.14 m
Material. Secondary M2: ZeroDur
Diameter. Tertiary M3: 0.15 x 0.11 m (elliptical flat)
Mount: Alt-Azimuth mount
First Light date: AT1: 24 January 2004, AT2: 2 February 2005, AT3: 1 November 2005, AT4: 15 December 2006
Active Optics: yes (passive M1, hexapod control of M2)
Adaptive Optics: in future NAOMI
Interferometry: UT & AT maximum 202 m baseline
Images of the ATs: Link
Press Releases with the ATs: Link