#astrophysics

• Aldebaran — The brightest star in the constellation of Taurus (Alpha Tauri) and the fourteenth-brightest star in the night sky, located approximately 65 light-years from Earth. It is a red giant star, much cooler than the Sun, but with a diameter about 44 times larger, easily recognizable due to its distinct reddish-orange hue.
• Ambartsumian — A surname of Armenian origin, globally famous due to the Soviet Armenian astrophysicist Viktor Ambartsumian. He was a pioneer of theoretical astrophysics, founder of the Byurakan Observatory, and renowned for discovering stellar associations and studying galactic evolution.
• Light-year — A unit of measurement for enormous astronomical distances, defined as the length of the path traveled by a beam of light in a vacuum within one Julian year. The value of a light-year is approximately 9.46 trillion kilometers; the term is often used figuratively to express a huge difference, an insurmountable cultural distance, or a massive technological gap between two entities.
• Anagalactic — Located, occurring, or extending beyond the limits of our galaxy (the Milky Way); situated in extragalactic space. In a cosmic structural sense, the term applies to celestial objects, radiations, or astronomical phenomena (such as nebulae, galaxy clusters, or cosmic rays) that originate or evolve outside the stellar system to which Earth belongs.
• Andromeda — A heroine in Greek mythology, daughter of King Cepheus and Cassiopeia, rescued from a sea monster by Perseus. In modern astronomy, the term designates a northern constellation and, notably, the Andromeda Galaxy (M31), a massive spiral galaxy located structurally as the Milky Way's closest major galactic neighbor.
• Annihilation — A fundamental physical process of interaction and complete conversion of the mass of an elementary particle and its corresponding antiparticle into radiant energy (high-frequency photons) upon their collision. This phenomenon represents a specialized terminological variant for annihilation, being utilized primarily in astrophysics and quantum physics to describe early structural universe reactions or gamma radiation emissions from active galactic nuclei.
• Antapex — An imaginary point on the celestial sphere, located in the constellation Columba, away from which the solar system moves in its global galactic motion relative to nearby stars. This astronomical structural element is located exactly one hundred and eighty degrees away, being diametrically opposed to the solar apex.
• Antares — The brightest star in the constellation Scorpius and one of the largest known stars, classified as a red supergiant in the advanced stages of its stellar evolution. Due to its distinct reddish-orange hue and its position in the night sky near the ecliptic, its name originates from Ancient Greek, meaning 'rival of Mars', as it was often visually confused with the planet.
• Antigravity — A hypothetical phenomenon consisting of the cancellation, inversion, or neutralization of the gravitational attraction force exerted by a massive body; gravitational repulsion. In modern theoretical physics, the concept is analyzed in relation to dark energy or negative mass hypotheses.
• Anti-gravitational — Tending to cancel, counteract, or reverse the effect of the gravitational attraction force; pertaining to antigravity. In theoretical cosmology, it describes mechanical properties of dark energy, which exerts a negative pressure with an anti-gravitational effect at a cosmic scale.
• Antiworld — A hypothetical world, parallel universe, or symmetrical cosmic region structurally composed entirely of antimatter, where atoms are formed by antiprotons, antineutrons, and positrons. In a theoretical sense, a direct structural collision between our world and an antiworld would generate a process of total annihilation, releasing an immense amount of energy in the form of gamma rays.
• Antimatter — A form of matter composed of antiparticles corresponding to ordinary particles, having the same mass and lifespan as them, but opposite electric charges and magnetic moments (e.g., positrons, antiprotons, antineutrons). In a structural sense, the direct interaction between matter and antimatter instantly leads to the process of mutual annihilation, with the complete conversion of mass into high-frequency radiant energy.
• Antimolecule — A hypothetical or experimentally synthesized molecular formation in high-energy laboratories, structurally composed entirely of antiparticles (antiprotons, antineutrons, and positrons) bound by the same electromagnetic and nuclear forces as an ordinary molecule. Direct contact between a molecule and an antimolecule triggers an instantaneous process of quantum annihilation with a massive release of gamma photons.
• Antilunar point — A hypothetical or real point on the celestial sphere or Earth's surface located in direct opposition (180 geometric degrees away) to the Moon (Selene). In a structural sense, it defines the axis diametrically opposite to the lunar vector, utilized in celestial mechanics calculations to determine antipodal gravitational resonance points or in astronomical meteorology to locate rare optical phenomena reflected symmetrically to the natural satellite's position.
• Apogalacticon — The point in the elliptical orbit of a star, a stellar cluster, or a celestial body orbiting a galaxy's nucleus that is farthest from the galactic center; galactic apoapsis. In stellar dynamics, this point represents the moment when the body's orbital velocity reaches its minimum value due to the maximum distance from the central mass.
• Arcturus — The proper name of the brightest star in the constellation Boötes and the fourth-brightest star in the entire night sky, being an orange giant located approximately 36.7 light-years from Earth. In mythology, the name originates from ancient Greek and means 'guardian of the bear', due to its structural proximity to the Ursa Major constellation.
• Astrophysical — Belonging to astrophysics, relating to astrophysics; referring to the application of the laws, methods, and principles of physics to the study of the structure, chemical composition, evolution, and dynamic phenomena of celestial bodies (stars, planets, galaxies, black holes) and interstellar space. It also defines the instruments, research, or mathematical models used to explain the behavior of matter and energy on a cosmic scale.
• Astrophysics — A branch of astronomy and modern physics that studies the physical properties, chemical composition, structure, dynamics, and evolution of celestial bodies (stars, planets, galaxies, nebulae) as well as the interstellar or intergalactic medium. This discipline applies the laws of thermodynamics, quantum mechanics, relativity, and electromagnetism to explain complex cosmic phenomena, from stellar nuclear fusion processes to cosmic microwave background radiation.
• 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.
• Astrophysicist — A woman who works as an astrophysicist; a highly qualified female researcher or specialist in the field of astrophysics who applies physical laws and principles to study the chemical composition, internal structure, orbital dynamics, and evolution of celestial bodies. Her activity involves utilizing high-power spectrographs, interpreting gravitational anomalies around black holes, and developing computational mathematical models to explain the expansion of the universe.