Figure: The Four ATs at Paranal

On the night of 15 December 2006, the fourth and last-to-be-installed VLTI Auxiliary Telescope (AT4) obtained its "First Light". The first images demonstrate that AT4 will be able to deliver the excellent image quality already delivered by the first three ATs. It will soon join its siblings to perform routinely interferometric measurements.

Credit: European Southern Observatory (ESO)

http://www.eso.org/esopia/images/html/phot-51c-06.html