Differences in proper motion between the primary (TGAS) solution and the Tycho-2 catalogue for 1 997 003 sources: a) differences in μα ∗; b) differences in μδ; and c) total differences . Differences are taken in the sense TGAS minus Tycho-2, after rotation of the latter to the Gaia DR1 reference frame. Median differences are shown in cells of about 0.84 deg2. Some empty cells are shown in white. The maps use an Aitoff projection in equatorial (ICRS) coordinates, with origin α = δ = 0 at the centre and α increasing from right to left.
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