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Published online by Cambridge University Press: 07 August 2017
Results from a complete survey of proper motions to B = 22.5 at the North Galactic Pole are summarized. Evidence from this and other surveys indicates that (1) the thick disk may extend to as much as 5.5 kpc above the Galactic plane at the solar radius, and (2) the thick disk may contain stars with metallicities as low as [Fe/H] = −1.6 or lower. These two properties of the thick disk mean that surveys of halo stars risk serious contamination by thick disk stars unless very conservative selection criteria are used. Applying these conservative selection criteria to existing surveys of halo stars reveals a surprising result - namely, that the halo is in retrograde rotation.