Planck scanning the Sky

Click here for more views of the way Planck scans the sky



As Planck spins on its axis it observes a ring around the sky. Over the course of the year, the axis around which Planck spins moves around the sky, ensuring that the satellite is never looking towards the Sun or the Earth. An example of a ring around the sky is shown on the right, and a daily-update can be found on the Planck Daily Status site, but animated movies are shown below.

Around once every hour the thrusters fire a short burst to push the satellite round a tiny amount. The angles by which it turns are very small, and add up to only around 1^o per day, but over the course of a year Planck goes the full 360^o around the Sun. Since every ring has two sides it scans almost every part of the sky twice in that year.

The detectors of Planck don't point quite at 90^o to the spin axis, but instead around 85^o. This means that to see the whole sky, the orbit of Planck must wobble a little bit - this is helped by the fact that Planck is actually orbiting the L2 point, rather than sitting in one place.

All of this means that Planck makes a slightly convoluted map of the sky, as shown in the movies below. The orientation of the map affects how it looks - the two movies below are shown in Ecliptic coordinates (aligned with the Earth's orbit around the Sun) and Galactic coordinates (aligned with the plane of our Galaxy). Both are shown in the "mollweide" projection, which is the standard projection for the CMB. This kind of projection maps the entire sky into a single oval shape, keeping all sizes and areas correct but distorting the shapes, particuarly around the edges.

Planck scanning the sky - all movies

Below are all the movies available for Planck's scanning of the sky. For each projection, the animation is shown in both Ecliptic and Galactic coordinates. Ecliptic coordinates are aligned with the Earth's orbit around the Sun, while Galactic coordinates are aligned with the plane of our Galaxy. In Ecliptic coordinates, the observed ring moves roughly right-to-left, with some small up-and-down wobble. In Galactic coordinates, it moves at an angle, as the Solar System (and therefore the Earth's orbit) is tilted with respect to our Galaxy.

Mollweide Projection

This projection maps the entire sky into a single oval, much like some maps of the world in atlases. The size and area of each point is preserved, but shapes are distorted, particularly around the edge.

http://planck.cf.ac.uk/scanning/all