astronaut noun A person who is trained to travel and work in a spacecraft. The astronaut spent six months conducting experiments aboard the space station. + astronomy noun The scientific study of stars, planets, and other objects in outer space. She majored in astronomy because she was fascinated by distant galaxies. + astronomer noun A scientist who studies stars, planets, and other objects and phenomena that occur outside Earth's atmosphere. The astronomer spent the night tracking a newly discovered comet through her telescope. + astronomic adjective Extremely large in size, amount, or degree, often used to emphasize how vast something is. The company racked up astronomic debts after years of reckless spending. + astronomical adjective Relating to astronomy, or so large in scale that it seems almost impossible to measure. The bridge was rebuilt at an astronomical cost that shocked local taxpayers. + astrophysics noun The branch of science that applies the laws of physics to explain stars, galaxies, and other cosmic phenomena. Her fascination with astrophysics began after she read about the discovery of black holes. + astrophysicist noun A scientist who studies the physical nature and behavior of stars, planets, and other celestial objects. The astrophysicist explained how neutron stars form after a massive star collapses. + astrophysical adjective Relating to the physical properties, processes, and behavior of stars, planets, and other objects in space. The paper described astrophysical conditions inside a collapsing star just before it becomes a black hole. + astrology noun The belief and practice of studying the positions of stars and planets to predict human affairs and events. She reads her horoscope every morning because she takes astrology seriously. + astrologer noun A person who studies the positions of stars and planets to predict human affairs. The astrologer told her that Mercury's position explained her recent bad luck. + astrological adjective Relating to astrology, the belief that star and planet positions influence human events. She checked her astrological chart before deciding whether to accept the job offer. + astrolabe noun A historical instrument used to measure the position of stars and calculate time or location. Sailors once used an astrolabe to determine their latitude by measuring the sun's angle. + astrocyte noun A star-shaped cell in the brain and spinal cord that supports and nourishes neurons. Astrocytes help regulate the chemical environment around neurons in the brain. + astrobiology noun The scientific study of the origin, evolution, and possible existence of life beyond Earth. The university's astrobiology program studies extreme environments where microbes might survive. + astrobiologist noun A scientist who studies the possibility and nature of life elsewhere in the universe. The astrobiologist analyzed samples from Mars for signs of ancient microbial life. + astrometry noun The branch of astronomy concerned with precisely measuring the positions, distances, and motions of stars and other celestial bodies. Astrometry allowed scientists to detect a tiny wobble in the star's position caused by an orbiting planet. + astrometric adjective Relating to the precise measurement of the positions and movements of stars and other celestial objects. The satellite collected astrometric data that pinpointed the star's exact position within a fraction of a second. + astronautics noun The science and technology of designing, building, and operating spacecraft for travel beyond Earth's atmosphere. She studied astronautics in college, focusing on the engineering behind rocket propulsion systems. + astrodynamics noun The study of the motion of spacecraft and other objects moving through space. Engineers relied on astrodynamics to calculate the probe's path to the outer planets. + astrochemistry noun The study of the chemical composition and reactions of matter found in space. Astrochemistry helped researchers identify complex organic molecules drifting inside a distant nebula. + astrogeology noun The study of the geology of planets, moons, and other bodies beyond Earth. Astrogeology helped scientists explain the volcanic history visible on the surface of Mars. + astroturf noun Synthetic grass-like material used to cover sports fields and other surfaces instead of natural grass. The stadium replaced its worn natural grass with durable green astroturf. + astroturfing noun The deceptive practice of disguising an organized campaign as spontaneous grassroots support from ordinary people. Journalists uncovered astroturfing behind what appeared to be an independent local protest. + astrophotography noun The specialized practice of photographing stars, planets, and other astronomical objects, often using long exposures. He drove far from city lights to practice astrophotography under a clear, dark sky. +