Scanning the microwave sky with Planck
This animation shows ESA's Planck observatory scanning the sky and completing its first all-sky survey.
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 the first all-sky image, obtained by using data spanning the full frequency range of Planck, which covers the electromagnetic spectrum from 30 to 857 GHz, both major emission sources in the microwave sky are evident: the grainy structure of the CMB, with its tiny temperature fluctuations reflecting the primordial density variations from which the cosmic web originated, is clearly visible at high latitudes, whereas the diffuse emission from gas and dust in the Milky Way dominates the low-latitude regions, extending well above and below the galactic plane.
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