Free Astronomy Magazine March-April 2018

MARCH-APRIL 2018 her- ent focus to feed a sin gle instrument!” When all four 8.2-metre Unit Telescopes combine their light-col- lecting power to feed a single instru- ment, the VLT effectively becomes the largest optical telescope in the world in terms of collecting area. Two of the main scientific goals of ESPRESSO are the discovery and char- acterisation of Earth-like planets and the search for possible variability of the fundamental constants of phys- ics. The latter experiments in partic- ular require the observation of distant and faint quasars, and this science goal will benefit the most from combining the light from all four Unit Tele- scopes in ESPRESSO. Both rely on the ultra-high stability of the instru- ment and an extremely stable refer- ence light source. Due to the com- plexity involved, the combination of ESO’s VLT working as 16 for first time by ESO O ne of the original design goals of ESO’s Very Large Telescope (VLT) was for its four Unit Tele- scopes (UTs) to work together to create a sin- gle giant tele- scope. With the first light of the ESPRESSO spec- trograph using the four-Unit- Telescope mode of the VLT, this milestone has now been reached. After extensive prepara- tions by the ESPRESSO con- sortium (led by the Astronomical Observatory of the University of Geneva, with the participation of re- search centres from Italy, Portugal, Spain and Switzerland) and ESO staff, ESO’s Director General Xavier Barcons initiated this historic astro- nomical observation with the push of a button in the control room. ESPRESSO instrument scientist at ESO, Gaspare Lo Curto, explains the historical significance of this event: “ESO has realised a dream that dates back to the time when the VLT was conceived in the 1980s: bringing the light from all four Unit Telescopes on Cerro Paranal together at an inco-