Zero: As a mathematical idea, the absolute zero obtained by the subtraction of equal quantities (expressed by a - a). In physical measurement, a lower limit or point of origin, as in the zero of a scale or the absolute zero of temperature.

As a symbol, the absence of all number or quantity, necessary in our system of notation in order to preserve the principle of positional value by occupying positions which would otherwise be filled by one of the nine digits.

Its symbol, the circle, represents at once nothing and everything; it is the symbol of boundless infinity; and a circle may be defined either as a single undivided and unterminated line, or as an infinite number of infinitely short lines.

Zodiac: The zone extending on both sides of the ecliptic, with a total width of about 16 degrees, so as to include the paths of the planets and moon. It is divided into twelve equal parts or signs, which are counted from the position of the vernal equinoctial point. The position of this point recedes westward along the ecliptic at the rate of about 50" of arc per year. The Hindus call this the fixed zodiac, giving the name of movable zodiac to the zodiacal constellations. The ancient figure for the length of a precessional cycle is 25,920 years, also the length of an important racial unit in human evolution.

Time is marked by the passage of the planets through its signs, by their conjunctions in various positions, and by the movement of the nodes and apsides of planets; so that the whole course of cycles large and small can be calculated and the past and future read by those who understand. The twelve divisions of the ecliptic or fixed zodiac have the same names and significance as the zodiacal constellations.