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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 Cy·cle n.
 1. An imaginary circle or orbit in the heavens; one of the celestial spheres.
 2. An interval of time in which a certain succession of events or phenomena is completed, and then returns again and again, uniformly and continually in the same order; a periodical space of time marked by the recurrence of something peculiar; as, the cycle of the seasons, or of the year.
    Wages . . . bear a full proportion . . . to the medium of provision during the last bad cycle of twenty years.   --Burke.
 3. An age; a long period of time.
    Better fifty years of Europe than a cycle of Cathay.   --Tennyson.
 4. An orderly list for a given time; a calendar. [Obs.]
    We . . . present our gardeners with a complete cycle of what is requisite to be done throughout every month of the year.   --Evelyn.
 5. The circle of subjects connected with the exploits of the hero or heroes of some particular period which have served as a popular theme for poetry, as the legend of Arthur and the knights of the Round Table, and that of Charlemagne and his paladins.
 6. Bot. One entire round in a circle or a spire; as, a cycle or set of leaves.
 7. A bicycle or tricycle, or other light velocipede.
 9. Thermodynamics A series of operations in which heat is imparted to (or taken away from) a working substance which by its expansion gives up a part of its internal energy in the form of mechanical work (or being compressed increases its internal energy) and is again brought back to its original state.
 10. Technology A complete positive and negative, or forward and reverse, action of any periodic process, such as a vibration, an electric field oscillation, or a current alternation; one period. Hence: Elec. A complete positive and negative wave of an alternating current. The number of cycles (per second) is a measure of the frequency of an alternating current.
 Calippic cycle, a period of 76 years, or four Metonic cycles; -- so called from Calippus, who proposed it as an improvement on the Metonic cycle.
 Cycle of eclipses, a period of about 6,586 days, the time of revolution of the moon's node; -- called Saros by the Chaldeans.
 Cycle of indiction, a period of 15 years, employed in Roman and ecclesiastical chronology, not founded on any astronomical period, but having reference to certain judicial acts which took place at stated epochs under the Greek emperors.
 Cycle of the moon, or Metonic cycle, a period of 19 years, after the lapse of which the new and full moon returns to the same day of the year; -- so called from Meton, who first proposed it.
 Cycle of the sun, Solar cycle, a period of 28 years, at the end of which time the days of the month return to the same days of the week. The dominical or Sunday letter follows the same order; hence the solar cycle is also called the cycle of the Sunday letter. In the Gregorian calendar the solar cycle is in general interrupted at the end of the century.


 Do·min·ic·al a.
 1. Indicating, or pertaining to, the Lord's day, or Sunday.
 2. Relating to, or given by, our Lord; as, the dominical (or Lord's) prayer.
    Some words altered in the dominical Gospels.   --Fuller.
 Dominical altar Eccl., the high altar.
 Dominical letter, the letter which, in almanacs, denotes Sunday, or the Lord's day (dies Domini). The first seven letters of the alphabet are used for this purpose, the same letter standing for Sunday during a whole year (except in leap year, when the letter is changed at the end of February). After twenty-eight years the same letters return in the same order. The dominical letters go backwards one day every common year, and two every leap year; e. g., if the dominical letter of a common year be G, F will be the dominical letter for the next year. Called also Sunday letter.  Cf. Solar cycle, under Cycle, n.