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

1) A series of usually metal links passing through one another, used for various purposes.
2) A series of things connected or following in succession. → chain reaction; → proton-proton chain.

Chain, from O.Fr. chaeine, from L. catena "fetter."

Zanjir from Mid.Pers. zanjir "chain;" zanjiré, from zanjir + nuance suffix -é.

A succession of → nuclear fissions when the neutrons released by previous fissions produce other nuclear fissions which themselves cause other reactions and the reactions goes on increasing exponentially.

→ chain; → reaction.

A series of nuclear decays produced by successive → daughter products, when the daughters are themselves → radioactive. For example, the decay chain N₁→ N₂→ N₃→ ... in which the parent nuclide N₁ decays to the daughter N₂, which in turn decays to N₃. Each → radionuclide in the decay chain can → branch to more than one daughter.

→ decay; → chain.

A string of a dozen or so galaxies in the central region of the → Vigo cluster. The chain lies to the right of the cluster's dominant galaxy M87 and extends over nearly 2° on the sky. The chain's brightest galaxies are the lenticulars M84 and M86. At least seven galaxies in the chain appear to move coherently, although others appear to be superposed by chance.

→ Markarian; → chain.

A → stochastic process, based on the classical → random walk concept, in which the probabilities of occurrence of various future states depend only on the previous state of the system and not on any of earlier states. Also called Markov process and Markovian principle.

Named after Andrey Andreyevich Markov (1856-1922), a Russian mathematician, who introduced this model in 1906; → chain.

A method for sampling from → probability distributions using → Markov chains. MCMC methods are widely used in data modeling for → Bayesian inference and numerical integration in physics, chemistry, biology, statistics, and computer science.

→ Markov chain; → Monte Carlo Method.

A series of → thermonuclear reactions, taking place mainly in → low-mass stars, such as the Sun, which transforms four hydrogen nuclei (protons) into one helium (⁴He) nucleus and thereby generates energy in the stellar core. First, two protons (¹H) combine to form a → deuterium nucleus (²H) with the emission of a → positron (e⁺) and a → neutrino (ν): ¹H + ¹H → ²H + e⁺ + ν. The deuterium nucleus then rapidly captures another proton to form a helium-3 nucleus (³He), while emitting a → gamma ray (γ): ²H + ¹H → ³He + γ. There are three alternatives for the next step. In the PP I chain, occurring in 86% of the cases, two ³He nuclei fuse to a final ⁴He nucleus while two protons are released: ³He + ³He → ⁴He + ¹H + ¹H. The mass of the resulting ⁴He nucleus is less than the total mass of the four original protons used to produce ⁴He (→ mass defect). The difference, ~ 0.7% of the total mass of the protons, is converted into energy and radiated by the Sun. In this process, the Sun loses some 4 million tons of its mass each second. See also → CNO cycle.

→ proton; → chain.