Planck observes the sky in the frequency range from 30 GHz to 857 GHz. The central horizontal band is dust emission from our own galaxy, the Milky Way, with gas and dust emission extending to high galactic latitudes. Away from the galactic plane the red and yellow structure shows the small fluctuations in the Cosmic Microwave Background (CMB) radiation that was emitted when the universe was 380 000 years old. The fluctuations are caused by variations in the density of the universe, which over time have collapsed into the galaxies, stars, and planets we see today. Other prominent features in the image are the Andromeda galaxy, visible as a sliver of light in the lower left quadrant, and the Large and Small Magellanic Clouds--satellite galaxies of the Milky Way, in the lower right quadrant of the image. Other more distant galaxies can be seen in the image as single points of light.
One of the goals of Planck is to measure the CMB and its polarization at high resolution over the entire sky. From these measurements we can determine the amount of normal matter in the universe, as well as the amount of dark matter--a substance that does not emit or reflect light, and dark energy which has been proposed to explain the accelerating expansion of the universe. Planck will enable us to search for evidence of primordial gravitational waves that may have been generated during inflation--a process theorized to have occurred a fraction of a second after the Big Bang. Observations of distant galaxies and galaxy clusters will enable us to study the origin of structure in the universe and investigate how and when stars form in the earliest galaxies.
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The microwave sky as seen by Planck. Image credit: ESA/NASA.