Surface number density of stars of the Hyades (cluster plus the two tidal arms). Each dot represents one star. The local number density is calculated with the sixth-nearest neighbour method (Casertano & Hut 1985) and is colour-coded. The black arrow indicates the velocity vector of the Hyades star cluster in the Galactic rest frame. The centre of the star cluster is located at the intersection of the two thin dashed lines.