The VLT uses active optics to reduce the effect of atmospheric turbulence on observations. In this technique the optical quality of a star is continually monitored against a reference star and the surface of the mirror adjusted to ensure that the image remains focused at all times. Similar adjustments are made to counteract the effects of gravity on the mirror. These techniques will allow each individual telescope to see objects 15 million times dimmer than the faintest stars visible to the naked eye.

Tests carried out by the ESO astronomers last week on the first of the telescopes to be completed - called UT1 - indicate that the 0.38 arc second resolution is better than expected For example, the test image of the Clover Leaf quasar is one of the best ground-based images of this object ever obtained. Testing on the telescope will continue until April 1999, when the telescope will be opened to the astronomy community.