#telescope

• Afocal — Having no real focal point or a finite focal length; relating to an optical system configured so that light rays entering parallel also exit parallel. In applied optics, these systems modify beam diameter or visual angle without focusing light onto a screen.
• Alma — A proper feminine given name widely used internationally, originating from Latin where it means 'nourishing' or 'kind', or from Hungarian where it means 'apple'. In contemporary science, ALMA is the acronym for the 'Atacama Large Millimeter/submillimeter Array', the largest and most expensive ground-based radio telescope in the world, located in the Atacama Desert of Chile; it is also the name of a historical river in the Crimean Peninsula.
• altazimuth — An astronomical instrument or mechanical mount utilized for determining the position of celestial bodies or for guiding telescopes and cameras, structurally characterized by rotation around two perpendicular axes: a horizontal axis (for measuring altitude or height above the horizon) and a vertical axis (for measuring azimuth).
• Arecibo — A proper geographical name designating a coastal municipality in Puerto Rico, globally famous for its iconic Arecibo Observatory, a massive astronomical structure built inside a natural sinkhole depression. Structurally, the observatory served for decades as a cornerstone in astrophysics, ionospheric research, and SETI programs searching for extraterrestrial intelligence, and was also the origin of the famous 'Arecibo Message' beamed into space in 1974.
• Astrodome — A transparent, hemispherical dome or cupola made of optical glass or durable plexiglass, mounted on the upper fuselage of an aircraft (especially 20th-century bombers and transport planes) or on a terrestrial structure. This structural element allowed the flight navigator to use a sextant or astrocompass to determine the position by observing celestial bodies, while in architecture it designates the rotating dome of a small astronomical observatory.
• Astrophysicist — A scientist, researcher, or highly qualified specialist in the field of astrophysics; an expert who applies the methods, theories, and principles of fundamental physics to investigate the structure, dynamic behavior, life cycles, and radiation of celestial bodies. Their activity includes spectral analysis of light emitted by stars, modeling collisions between black holes, or interpreting global gravitational anomalies.
• Astrophotographic — Belonging to astrophotography, relating to astrophotography; referring to the techniques, equipment, or processes used for photographing celestial bodies and cosmic phenomena. This term also describes optical instruments (such as refractors or telescopes) specifically designed to project a flat and color-corrected image directly onto a digital camera sensor.
• Astrograph — An astronomical refractor or telescope with a wide field of view, specifically designed and optimized for astrophotography, sky mapping, and astrometry. This optical instrument lacks an eyepiece for direct visual observation, instead focusing light directly onto a photographic plate (historically) or a large-scale electronic digital sensor (CCD/CMOS), enabling the precise recording of star and galaxy positions.
• 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.
• Astronomical — Belonging to astronomy, relating to astronomy; based on the laws, methods, and principles of studying celestial bodies. In colloquial, journalistic, or economic language, the term is used hyperbolically to describe a huge, exaggerated, substantial figure, sum of money, distance, or proportion that exceeds ordinary limits and recalls the vastness of cosmic dimensions.
• Astronomy — A fundamental and natural science that deals with the study, observation, measurement, and physico-mathematical interpretation of celestial bodies (stars, planets, satellites, comets, asteroids, galaxies), cosmic structures, and the universe as a whole. This discipline investigates the origin, evolution, chemical composition, and motion dynamics of matter and energy in extra-atmospheric space, being one of the oldest branches of human knowledge.
• Astroscopy — A rare and descriptive method or technique of direct observation and continuous visual examination of celestial bodies without automatic graphic or photographic recording. In a historical sense, the term referred to the qualitative study of stellar phenomena carried out by simply looking through the eyepiece of telescopes, being replaced in the modern era by spectroscopy and astrophotography.
• Atacama — A coastal desert located in northern Chile, South America, extending along a long plateau situated between the Andes and the Pacific Ocean. It is officially recognized as the driest desert in the world, excluding polar regions, being an essential site for global astronomy due to its extremely clear skies and high altitude, which hosts the largest terrestrial telescopes.
• Azimuthal — Pertaining to azimuth, belonging to azimuth, or carried out within the horizontal plane of the azimuth; often used to describe telescope mounts, map projections, or measuring instruments that utilize horizontal coordinates based on the angle formed with the North direction.