The Planck Satellite

Planck is the third Medium Size mission of the ESA Horizon 2000 Science Program. It is devoted to Cosmology and Astrophysics and will be launched in March 2007 together with Herschel Space Observatory. Planck is designed to image the anisotropies of the Cosmic Microwave Background Radiation (CMBR) over the whole sky, with unprecedented sensitivity and angular resolution. By scanning the sky with a 1.5 meter off-axis telescope, Planck will perform measurements at nine frequency channels between 25 GHz and 1 THz. The overview of the Planck programme and the instrument description is reported in this paper.