#positional astronomy

• Almucantar — A small circle on the celestial sphere parallel to the horizon, passing through all points that share the same angular altitude above it; an imaginary line used in positional astronomy and classic celestial navigation to measure and compare the vertical coordinates of celestial bodies.
• Astrometry — A fundamental branch of positional astronomy that deals with the precise geometric measurement of positions, proper motions, angular distances, and parallaxes of celestial bodies on the celestial sphere. This field establishes space reference systems and fundamental coordinates indispensable for galactic mapping, calculating planetary orbits, or detecting subtle gravitational perturbations generated by exoplanets.
• Astrometer — An astronomical measuring instrument used for the precise determination of angular positions, coordinates, and distances between celestial bodies in the night sky. Although historically the term defined filar micrometers or classic meridian circles used in astrometry, it can currently also designate the human specialists operating these complex mapping systems or automated scanning telescopes linked to sensor arrays.