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

An optical component or system for changing the image scale of a telescope to achieve a better match between the → seeing disk and the → pixel size.

→ focal; → reducer.

1) To bring to a certain state, condition, arrangement, etc.
Math.: To change the denomination or form, but not the value, of (a fraction, polynomial, etc.).
Chem.: To add an electron to.
2) To bring down to a smaller extent, size, amount, number, etc.; synonymous with → decrease.

M.E. reducen "to lead back," from O.Fr. reducer, from L. reducere, from → re- "back" + ducere "to bring, to lead."

From bâz-, → re- + Mid.Pers. hâxtan, hâzidan "to lead, guide, persuade," Av. hak-, hacaiti "to attach oneself to, to join," cf. Skt. sacate "accompanies, follows," Gk. hepesthai "to follow," L. sequi "to follow;" PIE *sekw- "to follow."
Kâstan, → decrease.

The "effective" → inertial mass appearing in the → two-body problem of → Newtonian mechanics. The reduced mass is a quantity which allows the two-body problem to be solved as if it were a one-body problem. For the masses m₁ and m₂, it is given by the ratio μ = m₁m₂ / (m₁ + m₂). The value of μ is generally smaller than m₁ and m₂. The larger the difference between the two masses, the closer μ will be to the smaller mass. If the particles are of equal mass, μ is half the mass of either.

→ reduce; → mass.

The → Planck constant divided by 2π and denoted ħ, pronounced h-bar. Also called the → Dirac constant.

Reduced, p.p. of → reduce; → Planck's constant.

→ reduced Planck constant.

→ reduced Planck constant.