From: Kirk
Herschel, the largest telescope ever launched, will study objects within and outside our Galaxy. It will be able to peer through clouds of gas and dust and observe stars as they form.Unlike Herschel, Planck will rotate continuously about its axis, scanning the whole sky to compile the most detailed and complete map ever of the Cosmic Microwave Background, or CMB. This CMB radiation is the relic radiation left over from the Big Bang, which occurred about 14 thousand million years ago.Herschel and Planck will be launched together atop an Ariane 5 rocket in spring 2009.