Doubling the Hipparcos star count: the Tycho-2 Catalogue
This starfield, 1 degree wide, includes a famous double star Alcor and Mizar (double white circle) in the tail of the Great Bear. The image is from the Digitized Sky Survey based on a red Palomar Schmidt plate. New Tycho-2 stars are marked with blue squares. Stars that are in both the Hipparcos Catalogue and Tycho-2 have white circles, while stars in both the first and the second Tycho catalogues are flagged with black circles. The faintest Tycho-2 stars in this field are of magnitude 12.4.