Phase

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Phase

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1. Of a periodic quantity, for a particular value of the independent variable, the fractional part of a period through which the independent variable has advanced, measured from an arbitrary reference. </dd>
The arbitrary reference is generally so chosen that the fraction is less than unity. In case of a simple harmonic quantity, the reference is often taken as the last previous passage through zero from the negative to positive direction. Thus, if two wave crest one-fourth cycle apart, they are said to be 90 degrees apart in phase, or 90 degrees out of phase. The moon is said to be at first quarter when it has completed one-fourth of its cycle from new moon. [[/a>|/a> ]]
2. The stage of aggregation of a substance, for example solid, liquid, or gas. </dd>
3. The extent to which the disk of the moon or the planet, as seen from the earth, is illuminated or not illuminated by the sun. </dd>
4. In astronomy = configuration. [[/a>|/a> ]]

References

This article is based on NASA's Dictionary of Technical Terms for Aerospace Use