Date: 25 Mar 2010
Copyright: C. North/Cardiff University & NASA/WMAP Science Team (background image)

From its orbit around the second Lagrange point (L2) of the Sun-Earth system, Planck performs a continuous scan of the sky. The spacecraft spins at 1 rpm causing the telescope's field-of-view, which is inclined at 85° to the spin axis, to trace out approximate great circles on the celestial sphere.

Planck's spin axis is periodically shifted by a few arcminutes per hour in ecliptic longitude (adding up to ~1° per day), to maintain an anti-Sun pointing throughout the year. As a result the annular region observed with the telescope slowly drifts across the sky, resulting in a complete sky survey.

In this animation the annular region observed by Planck at a given date is indicated in white. As a result of the selected map projection this appears as a curved line. Depicted in blue is the total area already covered, revealing a map of the microwave sky. (This map was produced with the Wilkinson Microwave Anisotropy Probe, WMAP.)

The projection used here is the Mollweide projection. This maps the entire sky into a single oval shape, preserving relative sizes and areas. The black grid shows Galactic coordinates, with the Galactic centre at the origin.

A similar animation using an orthographic projection instead of a Mollweide one is also available - see the related video in the right-hand menu.