  We address three major questions in astronomy, namely the detection of
biosignatures on habitable exoplanets, the geophysics of exoplanets and
cosmology. To achieve this goal, two requirements are needed. First a very
large aperture to detect spectro-polarimetric and spatial features of faint
objects such as exoplanets, and second a continuous monitoring to characterize
the temporal behavior of exoplanets such as rotation period, meteorology and
seasons. An Earth-based telescope is not suited for continuous monitoring and
the atmosphere limits the ultimate angular resolution and
spectro-polarimetrical domain. Moreover, a space telescope in orbit is limited
in aperture, to perhaps 15 m over the next several decades. This is why we
propose an OWL-class lunar telescope with a 50-100 m aperture for visible and
infrared (IR) astronomy, based on ESO's Overwhelmingly Large Telescope concept,
unachievable on Earth for technical issues such as wind stress that are not
relevant for a lunar platform. It will be installed near the south pole of the
Moon to allow continuous target monitoring. The low gravity of the Moon will
facilitate its building and manoeuvring, compared to Earth-based telescopes. As
a guaranteed by-product, such a large lunar telescope will allow Intensity
Interferometric measurements when coupled with large Earth-based telescopes,
leading to pico-second angular resolution.
