WHT time lost to technical problems

The plot below shows for each month the fraction of night between dusk and dawn astronomical twilights when the planned observations could not be carried out due to technical problems. Engineering/commissioning nights, service/discretionary nights and nights when observers were using their own instrument, are excluded from the data. The raw data (more up-to-date) from which the plot was constructed are here.

The fraction of time lost to technical problems declined rapidly after 1992, as newly-commissioned instruments and software systems settled in. It has been around 2 - 3% since then, apart from 1998-9, when a lot of time was lost to faults in an ageing data-acquisition system. The downtime is due to faults occurring in many different sub-systems, and is not easily reduced. Technical downtime at other 4-m telescopes is similar: As of the late 1990s, 3 - 4% was quoted for all of AAT, CTIO, KPNO, MMT and UKIRT.

1998 Feb 25, last revised 2009 Mar 23