Phase

Phase Phase (f[=a]z), n.; pl. {Phases} (f[=a]z"[e^]z). [NL. phasis, Gr. ?, fr. ? to make to appear: cf. F. phase. See {Phenomenon}, {Phantom}, and {Emphasis}.] 1. That which is exhibited to the eye; the appearance which anything manifests, especially any one among different and varying appearances of the same object. [1913 Webster]

2. Any appearance or aspect of an object of mental apprehension or view; as, the problem has many phases. [1913 Webster]

3. (Astron.) A particular appearance or state in a regularly recurring cycle of changes with respect to quantity of illumination or form of enlightened disk; as, the phases of the moon or planets. See Illust. under {Moon}. [1913 Webster]

4. (Physics) Any one point or portion in a recurring series of changes, as in the changes of motion of one of the particles constituting a wave or vibration; one portion of a series of such changes, in distinction from a contrasted portion, as the portion on one side of a position of equilibrium, in contrast with that on the opposite side. [1913 Webster]

5. (Phys. Chem.) A homogenous, physically distinct portion of matter in a system not homogeneous; as, the three phases, ice, water, and aqueous vapor. A phase may be either a single chemical substance or a mixture, as of gases. [Webster 1913 Suppl.]

6. (Zo["o]l.) In certain birds and mammals, one of two or more color variations characteristic of the species, but independent of the ordinary seasonal and sexual differences, and often also of age. Some of the herons which appear in white and colored phases, and certain squirrels which are sometimes uniformly blackish instead of the usual coloration, furnish examples. Color phases occur also in other animals, notably in butterflies. [Webster 1913 Suppl.]

7. (Elec.) The relation at any instant of a periodically varying electric magnitude, as electro-motive force, a current, etc., to its initial value as expressed in factorial parts of the complete cycle. It is usually expressed in angular measure, the cycle beb four right angles, or 360[deg]. Such periodic variations are generally well represented by sine curves; and phase relations are shown by the relative positions of the crests and hollows of such curves. Magnitudes which have the same phase are said to be in phase. [Webster 1913 Suppl.]

8. (Physics) the relation at any instant of any cyclically varying physical quantity, such as voltage in an A.C. circuit, an electromagnetic wave, a sound wave, or a rotating object, to its initial value as expressed as a fractional part of the complete cycle. It is usually expressed in angular measure, the complete cycle being 360[deg].

Note: The concept of phase is also applied generally to any periodically varying phenomenon, as the cycle of daylight. One person who speeps during the day and another who sleeps at noght may be said to be out of phase with each other. [PJC]