Gravitational lensing: From micro to nano

Different regimes of gravitational lensing depend on lens masses and roughly correspond to angular distance between images. If a gravitational lens has a typical stellar mass, this regime is named a microlensing because a typical angular distance between images is about microarcseconds in the case when sources and lenses are located at cosmological distances. An angular distance depends on a lens mass as a square root and therefore, if a lens has a typical Earth-like planet mass of 10-6M⊙, such a regime is called nanolensing. Thus, generally speaking, one can call a regime with a planet mass lens a nanolensing (independently on lens and source locations). So, one can name searches for planets with gravitational lens method a gravitational nanolensing. There are different methods for finding exoplanets such as radial spectral shifts, astrometrical measurements, transits, pulsar timing etc. Gravitational microlensing (including pixel-lensing) is among the most promising techniques if we are interested to find Earth-like planets at distances about a few astronomical units from the host star.