MIDI -: The 10 μm instrument on the VLTI

After more than five years of preparation, the mid-infrared interferometric instrument MIDI has been transported to Paranal where it will undergo testing and commissioning on the Very Large Telescope Interferometer VLTI from the end of 2002 through large part of this year 2003. Thereafter it will be available as a user instrument to perform interferometric observations over the 8 mum - 13 mum wavelength range, with a spatial resolution of typically 20 milliarcsec, a spectral resolution of up to 250, and an anticipated point source sensitivity of N = 3 - 4 mag or 1-2.5 Jy for self - fringe tracking, which will be the only observing mode during the first months of operation. We describe the layout of the instrument, laboratory tests, and expected performance, both for broadband and spectrally resolved observing modes. We also briefly outline the planned guaranteed time observations.