|Image Courtesy of Nick Wright|
The tiny stellar motions have to be deduced from high quality sky images obtained years apart. We at the University of Hertfordshire are at the forefront in this area, via our Galactic Plane surveys. Here, data from IPHAS (INT Photometric Hα Survey of the Northern Galactic Plane) steps in. This is the first comprehensive kinematic study of the massive northern OB association, known as Cyg OB2. The results portray a complex hierarchical structure, at odds with simple dispersal.