Planck sky coverage - Orthographic projection
Date: 24 March 2010
Copyright: C. North/Cardiff University & NASA/WMAP Science Team (background image)
This animation shows the evolution of the sky coverage by Planck from August 2009 to August 2010. It is based on predicted spacecraft pointings, which closely match the actual spacecraft pointings.
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 two curves. 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 orthographic projection, which maps the sky globe onto two halves. The black grid shows Galactic coordinates, with the left half of the sky globe centred on the Galactic centre and the right half on Galactic longitude 180°.
A similar animation using the Mollweide projection (the standard projection for maps of the Cosmic Microwave Background) instead of an orthographic one is also available - see the related video in the right-hand menu.
