Astrometrically

Astrometrically refers to measurements and analyses associated with astrometry, the branch of astronomy concerned with the precise positions and motions of celestial objects. An astrometric measurement determines where an object is in the sky, how it moves over time, and its distance via parallax. The term is used to distinguish geometric, position-based results from spectroscopic or photometric measurements.

Astrometric data are tied to a celestial reference frame, most commonly the International Celestial Reference System (ICRS), via reference objects such as distant quasars. Observations may be ground-based or space-based, using techniques from direct imaging to very long baseline interferometry. Parallax yields distance; proper motion yields transverse velocity; combined with radial velocity, full space motion can be inferred.

Prominent programs include the Hipparcos mission and the Gaia space observatory, which deliver large astrometric catalogs with microarcsecond precision. Astrometry underpins distance measurements, mapping of the Milky Way's structure, and the detection of exoplanets through astrometric wobbles. The adjective "astrometric" is sometimes used as well, but "astrometrically" is most often used to describe analyses or results performed in this framework.