Vertical circle, one that passes through the zenith and nadir of the celestial sphere. The prime vertical circle passes through the east and west points of the horizon.
Vulcan, discovery of, [137].
Worlds, the, and the Word, teach the same truth, [231-245].
Year, the, length of, on any planet, is determined by the periodic time.
Zenith, the point in the celestial sphere directly overhead.
Zodiac, a belt 18° wide encircling the heavens, the ecliptic being the middle. In this belt the larger planets always appear. In the older astronomy it was divided into twelve parts of 30° each, called signs of the zodiac.
Zodiacal light, [80].
Detach any of the following maps, appropriate to the time of year, hold it between you and a lantern out-of-doors, and you have an exact miniature of the sky. Or, better, cut squares of suitable sizes from the four sides of a box; put a map over each aperture; provide for ventilation, and turn the box over a lamp or candle out-of-doors. Use an opera glass to find the smaller stars, if one is accessible.
