Phase (redirected from phase feeding)

phase, in astronomy

phase, in astronomy, the measure of how much of the illuminated surface of a planet or satellite can be seen from a point at a distance from that body; the term is most often used to describe the moon as seen from the earth. When the moon is between the earth and the sun, we cannot see the lighted half at all, and the moon is said to be new. For a few days before and after the new moon we can see a small part of the lighted half, which appears as a crescent with the horns, or cusps, pointing away from the sun. When the moon has completed half its orbit from new moon to new moon, it is on the opposite side of the earth from the sun and we see the entire lighted half; this phase is called the full moon. When the moon is at quadrature with the sun, having completed either one quarter or three quarters of its orbit from new moon to new moon, half the lighted side is visible; this phase is called the half-moon. The half-moon between the new moon and the full moon is known as the first quarter and that between the full moon and new moon is known as the last quarter. Between the first quarter and the full moon and between the full moon and the last quarter we see more than half the lighted side; this phase is called gibbous. Of the planets, only Mercury and Venus, whose orbits pass between the earth and sun, show all the phases that the moon shows; the other planets are always either gibbous or full.

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phase, in physics

phase, in physics: see wave.

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phase

In thermodynamics, a chemically and physically uniform quantity of matter that can be separated mechanically from a nonhomogeneous mixture. It may consist of a single substance or of a mixture of substances. The three basic phases of matter are solid, liquid, and gas; other phases that are considered to exist include crystalline (see crystal), colloidal (see colloid), glass, amorphous, and plasma. The different phases of a pure substance are related to each other in terms of temperature and pressure. For example, if the temperature of a solid is raised enough, or the pressure is reduced enough, it will become a liquid.

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phase

In wave motion, the fraction of the time required to complete a full cycle that a point completes after last passing through the reference position. Two periodic motions are said to be in phase when corresponding points of each reach maximum or minimum displacements at the same time. If the crests of two waves pass the same point at the same time, they are in phase for that position. If the crest of one and the trough of the other pass the same point at the same time, the phase angles differ by 180° and the waves are said to be of opposite phase. Phase differences are important in alternating electric current technology (see alternating current).

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Phase (periodic phenomena)

The fractional part of a period through which the time variable of a periodic quantity (alternating electric current, vibration) has moved, as measured at any point in time from an arbitrary time origin. In the case of a sinusoidally varying quantity, the time origin is usually assumed to be the last point at which the quantity passed through a zero position from a negative to a positive direction.

In comparing the phase relationships at a given instant between two time-varying quantities, the phase of one is usually assumed to be zero, and the phase of the other is described, with respect to the first, as the fractional part of a period through which the second quantity must vary to achieve a zero of its own (see illustration). In this case, the fractional part of the period is usually expressed in terms of angular measure, with one period being equal to 360° or 2π radians. See Phase-angle measurement, Sine wave

An illustration of the meaning of phase for a sinusoidal wave

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1.		phase - The offset of one's waking-sleeping schedule with respect to the standard 24-hour cycle; a useful concept among people who often work at night and/or according to no fixed schedule. It is not uncommon to change one's phase by as much as 6 hours per day on a regular basis. "What's your phase?" "I've been getting in about 8 P.M. lately, but I'm going to wrap around to the day schedule by Friday." A person who is roughly 12 hours out of phase is sometimes said to be in "night mode". (The term "day mode" is also (but less frequently) used, meaning you're working 9 to 5 (or, more likely, 10 to 6).) The act of altering one's cycle is called "changing phase"; "phase shifting" has also been recently reported from Caltech.
2.		phase - "change phase the hard way": To stay awake for a very long time in order to get into a different phase.
3.		phase - "change phase the easy way": To stay asleep, etc. However, some claim that either staying awake longer or sleeping longer is easy, and that it is *shortening* your day or night that is really hard (see wrap around). The "jet lag" that afflicts travelers who cross many time-zone boundaries may be attributed to two distinct causes: the strain of travel per se, and the strain of changing phase. Hackers who suddenly find that they must change phase drastically in a short period of time, particularly the hard way, experience something very like jet lag without travelling.