Arne Ardeberg

ELT science drivers stress aperture, Strehl ratio, PSF definition andstability, field of view, wavelength range, flexibility, lowpolarisation and thermal emittance, auxiliary instruments, site andinfrastructure. Applicable science categories are planets and planetarysystems, stars and stellar systems, galaxies and galaxy clusters, andcosmology. ELT observations are needed for our own and other planetarysystems. The study of planetary disks and formation requires ELT data.ELT results, with emphasis on PSF quality and stability, are crucial tothe search for earth-like planets, especially those favourable for life.Investigation of star formation and stellar evolution requires ELTperformance, as does the study of final stellar stages. ELTs arenecessary for extremely high time resolution, details of stellarsurfaces and astroseismology. Galaxy formation studies will benefitdramatically from ELT data, as will studies of large-scale developmentof galaxies and galaxy clusters over cosmological time scales. Detectingactive galactic nuclei requires ELTs. ELT data are crucial for examiningthe structure and evolution of the universe. Observations of supernovaeand other standard sources over very large distances are necessary formapping the expansion of the universe and determining its accelerationor deceleration. Comparisons of Euro50 with VLTs and HST show a dramaticgain. The complementarity of Euro50, NGST and ALMA is noted.