The astronomy discovery space is dramatically widening with the operation, building and planning of new ambitious infrastructures. A key aspect for the scientific return of these facilities is the training of its users. Another important aspect is that the know-how to use the facilities is unevenly spread throughout Europe. The series of summer schools ONTHEFRINGE was designed to train a new generation of young astronomers on optical interferometry with the Very Large Telescope Interferometer, run by the European Southern Observatory, the top optical facility in the world.
The project consisted on a series of four two week schools with a strong practical, hands-on component. In the schools the theory of optical interferometry was presented and illustrated with practical applications and exercises that should be solved by the students in groups of two or three. At the end of the schools the groups of students presented their observational proposal for the Very Large Telescope Interferometer and received feedback from seasoned observers and colleagues. Two schools where of data reduction type and two of astrophysical type.The project was organized by putting in balance the European dimension of optical interferometry with the contribution of experts from third countries. Attendants of the school were selected on motivation letter, institute of origin and relevance to their research area/expertise. Given the uneven spreading of optical interferometry know-how in Europe preference was given to at least one attendant from one institute and from countries with lower know-how in the area. The gender balance was 33% female to 66% male, reflecting both astrophysics and the fact the most of the lecturers were male. 264 students attended the schools, the vast majority being PhD students (152) and young postdocs (56).