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

A problem raised in the past by observations suggesting that the amount of carbon necessary for standard → dust models was larger than what actually observed for the → interstellar medium (ISM) (Snow & Witt 1995). The problem was especially acute for the → 2175 A bump in the ultraviolet part of the → extinction curve. The so-called "crisis" was finally solved by, on the one hand, revising downward the → solar abundances, thought to represent the ISM abundances (Asplund et al. 2009, arXiv:0909.0948, and references therein), and, on the other hand, revising upward the ISM carbon abundances (Sofia et al., 2011, AJ 141, 22S).

→ carbon; → crisis.

1) A complex series of processes through which all the carbon atoms on Earth is cycled through the air, ground, plants, animals, and fossil fuels. During the cycle, plants absorb → carbon dioxide (CO₂) from the atmosphere and through → photosynthesis incorporate the associated carbon atoms into sugars and other molecules necessary for growth. Plants return carbon atoms back to the atmosphere in the form of CO₂. However, much of the carbon absorbed remains "locked up" in the living organisms until decomposition or fire releases it back to the atmosphere.
2) For nuclear fusion in stars → CNO cycle.

→ carbon; → cycle.

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.

A class of → red giant stars whose spectra show strong → molecular bands of → carbon compounds.

→ carbon; → star.

A radioactive isotope of carbon, whose nucleus contains 6 protons and 8 neutrons; also called → radiocarbon. ¹⁴C is naturally produced in the atmosphere when a neutron created by a cosmic ray hits the nucleus of an atom of nitrogen-14. The nucleus absorbs the neutron and ejects a proton, thereby transforming itself into ¹⁴C. It decays back to nitrogen, with a half-life is 5730 years, after emitting an electron (¹⁴₆C → ¹⁴₇N + e^- + ν_e). See also → radiocarbon dating.

→ carbon; → four + -teen, an inflected form of the root of → ten.

A star that presents very low → iron  → abundances [Fe/H] < -4 but an → anomalous richness in carbon. CEMP stars have been defined as a subset of → metal-poor stars that exhibit elevated [C/Fe] ≥ +1.0. It has been recognized that ~15-20% of stars with [Fe/H] < -2.0 are carbon enhanced. This fraction rises to 30% for [Fe/H] < -3.0, to 40% for [Fe/H] < -3.5, and ~75% for [Fe/H] < -4.0. This increasing trend of CEMP-star frequency with declining [Fe/H] is confirmed by the observation of many thousands of CEMP stars (Daniela Carollo + ApJ 2014, 788, 180). See also → extremely metal-poor star (EMPS)

→ carbon; → enhance; → metal; → metal; → poor; → star.

Containing or composed of carbon.

From → carbon + -aceous, from L. -aceus "-ous."

Karboni, adj. from karbon, → carbon; karbondâr "having carbon," with -dâr "having, possessor," from dâštan "to have, to possess;" O.Pers./Av. root dar- "to hold, keep back, maintain, keep in mind;" cf. Skt. dhr-, dharma- "law;" Gk. thronos "elevated seat, throne;" L. firmus "firm, stable;" Lith. daryti "to make;" PIE base *dher- "to hold, support."

A rare type of → stony meteorite having a higher → carbon content than other classes of meteorite. They represent only ~5% of the known meteorites. Their bulk composition is mainly → silicates, → oxides and sulfides, whilst the minerals → olivine and serpentine are characteristic. The six classes of carbonaceous chondrites are: → CI chondrites, CM chondrites, CV chondrites, CO chondrites, CK chondrites, CR chondrites, CH chondrites, and CB chondrites.

→ carbonaceous; → chondrite.

The radical -C=O, which occurs in several compounds, such as → aldehydes and ketones.

From → carbon + -yl a suffix used in the names of some radicals; → group.

Any of the four principal directions or points of the compass, → north, → east, → south, and → west. See also: → cardinal point.

→ cardinal; → direction.

A system for counting rotations of the Sun based on the mean → synodic rotation period of the Sun. Initially, Lord Carrington determined the solar rotation rate by watching low-latitude → sunspots. He defined a fixed solar coordinate system that rotates in a sidereal frame exactly once every 25.38 days. This means that the solar rotation period, as viewed from the Earth, is assumed to be constant. However, the synodic rotation rate varies during the year because of the changing speed of the Earth in its orbit and the mean synodic period is about 27.2753 days. Carrington rotation number 1 began on November 9, 1853.

Named for Richard C. Harrington (1826-1875), British astronomer, who initiated the system; → rotation.

A photon generation mechanism in an atom in which a transition initiates a series of secondary transitions from lower electronic levels.

→ cascade; → transition.

The main dark gap, 4,700 km wide, which divides Saturn's outermost A and B rings.

Named after Jean-Dominique Cassini (1625-1712), French astronomer of Italian origin, who discovered the division in 1675; → division.

Same as catalog place and → mean catalog place.

→ catalog; → position.

In a → syllogism, a → proposition or statement that deals with inclusion or exclusion of members of → subject classes in → predicate classes. Categorical propositions are of four basic forms, see → Aristotelian form.

→ categorical; → proposition.

Chemistry: A → positively charged → ion that is attracted to the → cathode in electrolysis. Any positively charged atom or group of atoms (opposed to → anion).

From cat-, → cathod, + → ion.

A relationship between the → refractive index (n) and the wavelength of light (λ) passing through a medium. It is commonly stated in the following form: n = A + B/λ² + C/λ⁴, where A, B, and C are constants characterizing the medium. The two-component Cauchy equation is n = A + B/λ², from which the dispersion becomes dn/dλ = -2B/λ³ showing that dispersion varies approximately as the inverse cube of the wavelength. The dispersion at 4000 A will be about 8 times as large as at 8000 Å.

Named after Augustin Louis Cauchy (1789-1857), French mathematician and physicist who found the first equation of dispersion in 1836; → equation.

1) The act or process of causing; the act or agency which produces an effect.
2) The relation of → cause to → effect.

Verbal noun from → cause.

A great circle on the → celestial sphere having a plane that passes through the center of the Earth at a right angle to the line formed by an observer's → zenith and → nadir.

→ celestial; → horizon.