The formation and evolution of galaxies is one of the key questions facing astronomers and cosmologists today.
How and when did the galaxies that light our Universe assemble their various components?
What kinds of galactic mergers and cannibalistic acquistions of smaller galaxies by their larger neighbors occurred as the Universe evolved?

Study of stars in the Milky Way galaxy is critical to understanding how galaxies form and evolve. Through study of galaxy formation, we test models of dark matter, gravitational collapse, hydrodynamics of the gas, stellar formation and feedback. The Milky Way is the only galaxy we can study in enough detail that these models can be tested in the six dimensions of phase-space. LEGUE was designed to study the structure of Galactic halo (both the smooth component of the spheroid and the lumpy sub-structure) and disk components (including star-forming regions and open clusters (OCs)).The revealed structure will improve models in terms of better understanding star formation, the formation history of Galaxy, and the structure of gravitational potential, including the central black hole and (sub) structure of dark matter component.