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

The act of linking together or forming couples; a connection between two things so they move together.
The quality of coupled systems or the way they are coupled.

Noun from → couple; → -ing.

A parameter that indicates the strength of the interaction between two systems.

→ coupling; → coefficient.

In nuclear physics, a constant that indicates a measure of how strongly two particles interact.

→ coupling; → constant.

Cosmology: In the early history of the Universe, separation of matter and radiation due to their non-interaction. At a redshift of 1000, that is about 400,000 years after the Big Bang, the temperature would have cooled to the point (4000 degrees Kelvin) where electrons and nuclei can recombine and form neutral hydrogen atoms. Since atoms do not scatter the radiation appreciably, free electrons were lacking, and the Universe became transparent to radiation. Same as → recombination. See also → decoupling era.

Verbal noun of decouple, from → de- + → couple + → -ing.

The era some 400,000 years after the → Big Bang, when the cosmic → blackbody radiation was last scattered by the matter. → decoupling. Same as → recombination era and → last scattering epoch.

→ decoupling; → era.

Same as → fine-structure constant.

→ electromagnetic; → coupling; → constant.

The dimensionless gravitational constant defined as the gravitational attraction between pair of electrons and normally given by: α_G = (Gm_e²) / (ħc) = (m_e / m_P)² ~ 1.7518 × 10^-45, where ħ is → Planck's reduced constant, c the → speed of light, m_e is the → electron mass, and m_P is the → Planck mass.

→ gravitational; → coupling; → constant.

A coupling scheme of electronic → spin angular momenta and → orbital angular momenta for heavy atoms (generally Z > 30), where the spin and orbital angular momenta of individual electrons couple strongly, and therefore the → LS coupling scheme does not apply. The coupling between spin and orbital angular momentum of each electron is much stronger than the coupling between different electrons. Therefore, the total angular momentum, j_i, for the i-th electron is obtained by combining l_i and s_i and then coupling these j's together to give the total angular momentum J = Σ_i j_i. In the jj coupling scheme the total orbital angular momentum quantum number, L, and the total spin angular momentum number, S, are not specified.

j referring to the symbol of the total angular momentum for individual electrons; → coupling.

Same as → Russell-Saunders coupling.

L referring to the total → orbital angular momentum and S to the total → spin angular momentum; → coupling.

A coupling scheme of → electron configuration, used mainly for the lighter atoms with → atomic number less than 30. In an atom when changes in energy states are produced by the action of two or more electrons, the value of the total angular momentum of these electrons results from the coupling between the total → orbital angular momenta of the electrons and the total → spin angular momenta of the electrons. In this scheme the orbital angular momenta and spin angular momenta of electrons are added separately to give the total angular momentum L = Σ_i l_i and the total electron spin angular momentum S = Σ_i s_i. These are then added to give J = L + S. Also called → LS coupling. See also → jj coupling.

After Henry Norris Russell (1877-1957) and Frederick Albert Saunders (1875-1963), American astronomers (1925, ApJ 61, 38); → coupling.

1) Astro.: A relationship between the orbital period of one body around another and its rotational period on its axis. The relationship results from tidal forces between the two bodies. For example, the rotation period of the Moon equals its revolution period around the Earth.
2) Quantum mechanics: The interaction between a particle's → spin angular momentum and its → orbital angular momentum.

→ spin; → orbit; → coupling.

In a system composed of one celestial body orbiting another, the synchronization of the orbital and rotational motions of the two bodies under the action of → tidal forces. For example, Pluto is tidally coupled to its moon Charon. As for the → Earth-Moon system, billions of years from now, the Earth and the Moon will have the same period of rotation, and these will also exactly equal the orbital period of the Moon around the Earth. → tidal friction.

→ tidal; → coupling.