grating, a high transmission volume phase holographic grating. This has given a throughput that peaks above 50% around 700-800 nm and exceeds 40% across almost the entire wavelength range of the instrument. The full instrument weighs close to eight metric tons and essentially fills the Nasmyth platform's volume of 50 m3. But due to the modular design, each of the 24 IFUs can be removed for maintenance or repair - in order to do this a special cradle was designed to safely remove and insert an IFU. Adaptive optics interface In order to achieve the required boost in spatial resolution across the celestial sphere, MUSE makes use of the GALACSI interface which is part of the Adaptive Optics Facility on UT4 at VLT. All the adaptive optics (AO) components are all mounted in the Nasmyth derotator and a metrology system is used to ensure alignment of the AO system with MUSE. This is needed since MUSE is located on the Nasmyth platform. Armed with the AO system, it is expected that MUSE will achieve a median spatial resolution of 0.46 arcseconds, or ~3 kpc at a redshift >3, across the 1'x1' field-of-view of the wide-field mode. In the narrow-field mode, the spatial resolution should reach 0.042 arcseconds at 750 nm, corresponding to ~3 pc resolution at the distance of Virgo Cluster of galaxies. Data rates and management Each exposure with MUSE will return a datafile with data from the 24 IFUs at 35 MB each - thus the total size of the raw datafile is 0.84 GB. After data reduction this will expand to a total of 3.2 GB per exposure as the data are translated into floating point values and an error estimate cube is produced. This means that observations that rely on many short exposures can produce very large datasets - easily producing 100 GB per night of fairly complex data. Operation and results Gallery References External links MUSE page in Lyon MUSE page at ESO The MUSE commissioning blog Spectrometers Telescope instruments European Southern Observatory Articles containing video clips