Astrometry: Measurement of the positions and motions of objects in the sky. The word astrometry derives from the Greek roots astro (the combining form of the Greek word 'a`stron, meaning star) and meter (measure).
Coronagraphy: A direct imaging technique that attenuates the light of a central source by means of opaque stops in the optical train. In our context the purpose of this technique is to enhance ability to measure the relatively dim light of circumstellar material or faint companions (e.g. planets) near bright, nearby stars.
Differential astrometry: Measurement of the relative angular separation of two (or more) objects in the sky.
Interferometer: A device that measures the interference (and related phenomena) of electromagnetic radiation (at least in our context).
Interference fringes: The interference of starlight (or other electromagnetic radiation) manifests itself as alternating regions of constructive and destructive interference in the space of relative propagation delay between the two arms of the interferometer. These alternating constructive and destructive regions are known as interference fringes.
Habitable zone: A region around a star where the physical conditions on planets in the region are conducive to life. Practically, we believe a habitable zone is one where the temperature is such that water remains in a liquid state a large fraction of the time.
Nulling: An interferometric technique that inverts the phase of the optical field in one arm of the interferometer relative to the other in order to attenuate the light of a central source. In our context the purpose of this technique is to enhance ability to measure the relatively dim light of diffuse circumstellar material or faint companions (e.g. planets) near bright, nearby stars.
Visibility: The attribute of interference fringes that describes the contrast between constructive (bright) and destructive (dark) interference regions. Mathematically visibility is a complex (phasor) quantity whose magnitude (modulus) quantifies the fringe contrast, and whose phase describes the position of the constructive and destructive interference regions relative to some reference. The visibility is related to brightness morphology that an interferometer measures, so visibilities can be used to synthesize an image or constrain morphological models of astronomical sources.