Gaia is the European Space Agency mission which will provide a stereoscopic census of our Galaxy through the measurement of high accuracy astrometry, radial velocities and multi-colour photometry. Gaia is scheduled for launch in August 2013. It is designed to map over one billion stars over the course of its five year mission, in practice every object in the sky brighter than magnitude 20. There are three instruments to collect astrometric, photometric and spectroscopic data on stars in the Milky Way and in galaxies belonging to the Local Group, distant galaxies, quasars and solar system objects. Gaia builds on the expertise established in Europe through the successful ESA Hipparcos mission. It will achieve an astrometric accuracy of 10–25 μas, depending on colour, at 15th magnitude and 100–300 μas at 20th magnitude. Multi-colour photometry will be obtained for all objects by means of low-resolution spectrophotometry between 330 and 1000 nm. In addition radial velocities with a precision of 1–15 km/s will be measured for all objects to 17th magnitude, thus complementing the astrometry to provide full six-dimensional phase space information for the brighter sources.

The GREAT initiative is a pan European science driven research infrastructure which will facilitate the fullest exploitation of the ESA Gaia 'cornerstone' astronomy mission, through focused interaction on a European scale. This will enable the European astronomical community to provide answers to the key challenges in our understanding of the Galaxy and Universe.

GREAT is the programme which will bring together relevant scientific expertise by promoting topical workshops, training events, exchange visits, conferences and so forth with the aim of addressing the major scientific issues that the Gaia satellite will impact upon. GREAT provides support through its European Science Foundation Research Networking Programme for a wide range of community proposed events covering the key objective areas of the programme, largely focussed on gaining a deeper understanding of our Milky Way.

As a major collaborative effort in GREAT, a join proposal was submitted to ESO in response to its call for Large Programmes. The proposal was selected by ESO and started operations in December 2011. The Gaia-ESO survey (GES) is a public spectroscopic survey that will observe more than 105 stars using FLAMES at the VLT. It will sample all major components of the Milky Way: halo, bulge, thin and thick discs, and open clusters of all ages and masses. It will provide a homogeneous overview of the distribution of kinematics and elemental abundances of the Galaxy, well beyond the Solar neighborhood. The Survey alone will have great impact on our knowledge of Galactic and stellar evolution. When combined with Gaia astrometry the Survey will quantify the formation history and evolution of young, mature and ancient Galactic populations.

The GREAT-ITN is a Marie-Curie Initial Training Network (ITN) which aims at preparing a generation of young researchers for the scientific exploitation of the Gaia catalogue data. The GREAT-ITN project will shape a critical mass of new expertise with the fundamental skills required to power the scientific exploitation of Gaia over the coming decade and beyond. The GREAT-ITN research theme is 'Unravelling the Milky Way' focused on four fundamental problems: unravelling the origin and history of our home galaxy; tracing the birth place and understanding the astrophysical properties of the stellar constituents of our galaxy; deepening the understanding of planetary systems by linking the study of exoplanets to the origins of the solar system; take up the grand challenges offered by Gaia in the domains of the distance scale and the transient sky.

The GREAT-ITN will deliver a training programme structured around these research themes to a core of new researchers, equipping them with the skills and expertise to become future leaders in astronomy or enter industry. These skills are relevant across many of the key challenges facing us now from climate change to energy security. These require well trained people, people which this GREAT-ITN will deliver.

It is as part of the training programme of GREAT-ITN that we are organising a school in Tenerife (Canary Island, Spain) aimed at providing the students with a deep understanding of all stages of a large observational project, from the conception, through planning organisation, management observations and reduction. The Canary Islands hosts the European Northern Observatory (ENO) composed by two major observatories located in the islands of Tenerife (OT) and La Palma (ORM), this latter being the site of the largest optical-infrared telescope in the world, the GTC. Both observatories are managed by the Instituto de Astrofísica de Canarias (IAC).

The school main aim is to provide the students with a background in the many details associated with a large observational project, like Gaia or the on going GES, which will be used as an example.