An Etymological Dictionary of Astronomy and Astrophysics
English-French-Persian

CO₂, also called carbonic acid gas. A colorless gas which occurs in the atmosphere playing an essential part in animal respiration and the growth of green plants. → photosynthesis, → carbon cycle. It is formed by the → oxidation of carbon and carbon compounds. Carbon dioxide is the most important → greenhouse gas produced by human activities, primarily through the combustion of fossil fuels. Its concentration in the Earth's atmosphere has risen by more than 30% since the Industrial Revolution. CO₂ forms a solid at -78.5 °C at atmospheric pressure, and is used as a refrigerant in this form as a dry ice for the preservation of frozen foods. As carbon dioxide gas is heavier than air and does not support combustion, it is used in fire extinguishers.
CO₂ is present in the → interstellar medium and is one of the main → molecules in → comets.

→ carbon; → dioxide.

A colorless, odorless, very poisonous gas which burns in air with a bright blue flame to form → carbon dioxide. CO gives rise to a violent explosion when ignited in air in certain proportions. It occurs in coal gas and in the exhaust fumes of motor engines. Melting point -207 °C; boiling point -191.1 °C.
Carbon monoxide is the most important → molecule found in the → interstellar medium, and is produced through several chemical reactions, → CO formation. It was discovered in 1970 by R. Wilson and A. Penzias of Bell Laboratories, using the 11-m telescope of the National Radio Astronomy Observatory (NRAO) in the direction of the → Orion nebula. Because the CO line is so intense and widely distributed in space, this molecule is a most useful tool for tracing the ISM. In addition, measurement of its rare isotopes have shown that the main line ¹²C¹⁶O (wavelength 2.6 mm, 115 GHz) is → optically thick, that is the → column density of the molecule is so high that the material becomes opaque at the transition frequency. Moreover, the upper-energy levels of the CO molecule are easily excited by collision with → molecular hydrogen. The combination of high → optical depth and the ease of → excitation imply that CO emission brightness will accurately reflect the local gas temperature. CO is also one of the principal molecules detected in → comet nuclei.

→ carbon; → mono-; → oxide.

Any → oxide containing two → atoms of → oxygen the → molecule.

→ di-; → oxide.

A diatomic ion containing one oxygen and one hydrogen atom with chemical formula OH^-.

→ hydr-; → oxide.

A compound of → oxygen and another → chemical element.

From Fr. oxyde, from oxygène, → oxygen and acide, → acid.

A → diatomic molecule made up of → titanium and → oxygen atoms. See → TiO band.

→ titanium; → band.

A black crystalline solid (UO_{2pitchblende, carnotite, and autunite and is used chiefly as a source of nuclear energy by fission of the radioisotope uranium-235. After the → uranium hexafluoride is enriched, a fuel fabricator converts it into uranium dioxide powder and presses the powder into fuel pellets.}

→ uranium; → dioxide.

A chemical compound made up of → uranium and → oxygen. The most common forms of uranium oxide are U₃O₈ and UO₂. Both oxide forms are solids that have low solubility in water and are relatively stable over a wide range of environmental conditions. Triuranium octaoxide (U₃O₈) is the most stable form of uranium and is the form most commonly found in nature. → Uranium dioxide (UO₂) is the form in which uranium is most commonly used as a → nuclear reactor fuel. At ambient temperatures, UO₂ will gradually convert to U₃O₈.

→ uranium; → oxide.

A → diatomic molecule made up of → zirconium and → oxygen atoms. See → ZrO band.

→ zirconium; → band.