Month n.  One of the twelve portions into which the year is divided; the twelfth part of a year, corresponding nearly to the length of a synodic revolution of the moon, -- whence the name.  In popular use, a period of four weeks is often called a month.
 Note: ☞ In the common law, a month is a lunar month, or twenty-eight days, unless otherwise expressed. --Blackstone. In the United States the rule of the common law is generally changed, and a month is declared to mean a calendar month. --Cooley's Blackstone.
 A month mind. (a) A strong or abnormal desire. [Obs.] --Shak. (b) A celebration made in remembrance of a deceased person a month after death. --Strype.
 Calendar months, the months as adjusted in the common or Gregorian calendar; April, June, September, and November, containing 30 days, and the rest 31, except February, which, in common years, has 28, and in leap years 29.
 Lunar month, the period of one revolution of the moon, particularly a synodical revolution; but several kinds are distinguished, as the synodical month, or period from one new moon to the next, in mean length 29 d. 12 h. 44 m. 2.87 s.; the nodical month, or time of revolution from one node to the same again, in length 27 d. 5 h. 5 m. 36 s.; the sidereal, or time of revolution from a star to the same again, equal to 27 d. 7 h. 43 m. 11.5 s.; the anomalistic, or time of revolution from perigee to perigee again, in length 27 d. 13 h. 18 m. 37.4 s.; and the tropical, or time of passing from any point of the ecliptic to the same again, equal to 27 d. 7 h. 43 m. 4.7 s.
 Solar month, the time in which the sun passes through one sign of the zodiac, in mean length 30 d. 10 h. 29 m. 4.1 s.

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 So·lar, a.
 1. Of or pertaining to the sun; proceeding from the sun; as, the solar system; solar light; solar rays; solar influence. See Solar system, below.
 2. Astrol. Born under the predominant influence of the sun. [Obs.]
    And proud beside, as solar people are.   --Dryden.
 3. Measured by the progress or revolution of the sun in the ecliptic; as, the solar year.
 4. Produced by the action of the sun, or peculiarly affected by its influence.
    They denominate some herbs solar, and some lunar.   --Bacon.
 Solar cycle. See under Cycle.
 Solar day. See Day, 2.
 Solar engine, an engine in which the energy of solar heat is used to produce motion, as in evaporating water for a steam engine, or expanding air for an air engine.
 Solar flowers Bot., flowers which open and shut daily at certain hours.
 Solar lamp, an argand lamp.
 Solar microscope, a microscope consisting essentially, first, of a mirror for reflecting a beam of sunlight through the tube, which sometimes is fixed in a window shutter; secondly, of a condenser, or large lens, for converging the beam upon the object; and, thirdly, of a small lens, or magnifier, for throwing an enlarged image of the object at its focus upon a screen in a dark room or in a darkened box.

 Solar month. See under Month.
 Solar oil, a paraffin oil used an illuminant and lubricant.
 Solar phosphori Physics, certain substances, as the diamond, siulphide of barium (Bolognese or Bologna phosphorus), calcium sulphide, etc., which become phosphorescent, and shine in the dark, after exposure to sunlight or other intense light.
 Solar plexus Anat., a nervous plexus situated in the dorsal and anterior part of the abdomen, consisting of several sympathetic ganglia with connecting and radiating nerve fibers; -- so called in allusion to the radiating nerve fibers.
 Solar spots. See Sun spots, under Sun.
 Solar system Astron., the sun, with the group of celestial bodies which, held by its attraction, revolve round it. The system comprises the major planets, with their satellites; the minor planets, or asteroids, and the comets; also, the meteorids, the matter that furnishes the zodiacal light, and the rings of Saturn. The satellites that revolve about the major planets are twenty-two in number, of which the Earth has one (see Moon.), Mars two, Jupiter five, Saturn nine, Uranus four, and Neptune one. The asteroids, between Mars and Jupiter, thus far discovered (1900), number about five hundred, the first four of which were found near the beginning of the century, and are called Ceres, Pallas, Juno, and Vesta.
 -- Solar telegraph, telegraph for signaling by flashes of reflected sunlight.
 Solar time. See Apparent time, under Time.

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 solar month
      n : one-twelfth of a solar or tropical year