What is the percentage of observations performed in visitor mode versus service mode, and what are the main advantages and disadvantages offered by each mode?
At present, most observations are done in service mode, at 60-70% of the total time, versus 30-40% for the visitor mode. Although the VLT is exclusively operated by highly specialised ESO staff, the visitor mode offers astronomers the opportunity for direct interaction, which is particularly useful whenever any real-time decision is needed; nevertheless, any time lost for meteorological reasons cannot be reassigned. On the other hand, the service mode guarantees full flexibility to reschedule observations to match them with the most suitable atmospheric conditions.
