Saturn completes the set
At the start of Janary 2010, Planck has observed Saturn, meaning that it has now observed the full set of planets. The planets are very useful objects for Planck to observe, as their brightness and small size makes them ideal for checking exactly where Planck's beams are pointing.
Planck can see the planets which orbit further out from the Sun: Mars, Jupiter, Uranus and Neptune. Because Planck is always looking more than 90o away from the Sun, it cannot seeVenus or Mecury as they orbit the Sun within the Earth's orbit and therefore never come into Planck's field of view
The movie below shows the ring Planck observes as is spins around, and the motion of that ring as Planck orbits the Sun out near the L2 point. The planets are marked on as white circles containing symbols. The key is: plus(+)=Mars, cross(X)=Jupiter, triangle=Saturn, square=Uranus, star(*)=Neptune. Notice that there's now a gap until around April before Planck observes another Planet (Mars again, as it happens). The gap is simply because of the way the planets are clustered on the sky. During the first survey Planck will observe each planet twice, roughly 6 months apart. I won't be exactly 6 months, though, as the planets move around the sky over the year - look at the speed Mars moves at!
Planck Images (ESA)
Planck Videos (ESA)
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