The Gaia Basic angle: measurement and variations A. Mora, U. Bastian, M. Biermann, F. Chassat, L. Lindegren, I. Serraller, E. Serpell and W. van Reeven EAS Publications Series, 67-68 (2014) 65-68 Published online: 17 July 2015 DOI: 10.1051/eas/1567010