The Cosmic Web Imager: an integral field spectrograph for the Hale Telescope at Palomar Observatory: instrument design and first results

We describe the Cosmic Web Imager (CWI), a UV-VIS integral eld spectrograph designed for the Hale 200" telescope at the Palomar Observatory. CWI has been built specically for the observation of diuse radiation. The instrument eld of view is 60"40" with spectral resolving power of R5000 and seeing limited spatial resolution. It utilizes volume phase holographic gratings and is intended to cover the spectral range 3800A to 9500A with an instantaneous bandwidth of 450A. CWI saw rst light in July 2009, and conducted its rst successful scientic observations in May 2010.