Astronometri

Astronometri, or astronometry in English, is the science of measuring the positions, motions, and distances of celestial objects. It is a fundamental branch of astrometry, centered on obtaining precise angular measurements and tracking how these positions change over time. Through these measurements, astronomers determine celestial coordinates, proper motions, parallaxes, and distance scales that underpin much of observational astronomy and astronomical navigation.

Historically, astronometri emerged from careful naked-eye observations and accurate timekeeping, but its modern methods began with the first successful stellar parallax measurement by Friedrich Bessel in 1838 for 61 Cygni. The development of photographic plates, then CCD detectors, enabled large catalogs of parallax and proper motion. In the late 20th century, ground-based programs expanded, and space-based missions dramatically increased accuracy and reach.

Key instruments and data sources include ground-based telescopes, interferometers, and satellite observatories. Notable milestones are the Hipparcos mission (1989–1993) and the Gaia mission (launched 2013), which have produced precise parallaxes and proper motions for hundreds of millions to over a billion stars. Celestial reference frames, such as the International Celestial Reference Frame, are built from measurements of distant quasars and radio sources using very long baseline interferometry.

Applications of astronometri include constructing the cosmic distance ladder, mapping the structure and dynamics of the Milky Way, determining stellar kinematics, and aiding spacecraft navigation. The field continues to underpin tests of fundamental physics and cosmology by providing accurate distance scales and motion data.

Modern astronometri combines high-precision instrumentation, robust statistical methods, and sophisticated data processing to produce three-dimensional maps of the nearby universe and to probe the geometry of our Galaxy.