Ðð Blockinøø Àà×øóöýý Óöññøøóò ² Úóðùøøóò

We explore the motivation behind large stellar surveys in Galactic astronomy, in particular, surveys that measure the photometric, phase space and abundance properties of thousands or millions of stars. These observations are essential to unravelling the sequence of events involved in galaxy formation and evolution, although disentangling key signatures from the complexity continues to be very challenging. The new data will require major advances in our understanding of stellar atmospheres, stellar chemistry, the dynamics of the Galaxy and the Local Group. 1. Galactic Surveys – Why Bother? In this Joint Discussion, we explore the motivation behind large surveys in Galactic astronomy. We focus our attention on surveys that measure the photometric, phase space or abundance properties of individual stars. In recent years, we have seen the release of optical and infrared all-sky photometric catalogues for ∼ 10 8 stars (SDSS: Gunn et al 2001; 2MASS: Cutri et al 2003), and new astro-metric catalogues from the Hipparcos satellite and the US Naval Observatory (UCAC2: Zacharias et al 2004). The first major kine-matic stellar survey of roughly 15,000 stars was recently completed by Nordstrom et al (2004), with two new much larger surveys now under way (RAVE: Steinmetz et al 2006; SEGUE: Rockosi 2005). There is ongoing discussion of extending these million-star surveys to 8m class telescopes early in the next decade Send offprint requests to: J. Bland-Hawthorn (WFMOS: Colless 2005). At that time, the European Space Agency is set to launch the Gaia astrometric satellite with a view to establishing phase space information for a billion stars (Perryman et al 2001; Wilkinson et al 2005). But why go to all this trouble? Increasingly, we are required to defend big survey machines with rigorous and compelling science cases, and these must be argued carefully within the context of " Big Questions " that are posted on the web sites of major funding agencies. In fact, it is probable that only one of these questions bears directly on galactic stellar surveys − the formation and evolution of galaxies. But here, a good case can be made, as we discuss below. It is no exaggeration to say that the study of galaxy formation and evolution will dominate observational cosmology and galactic studies for decades to come. This is because it is difficult to define a unique model for galaxy formation , assuming one even exists. A theoreti