Action. The way in which a thing works.

Affect. To act upon; to change; to be moved or influenced by.

Almanac. A pamphlet or book containing tables showing the days of the year; also the time the Sun and Moon rise and set; the conjunctions, eclipses and other information concerning the things in the sky. The word almanac is supposed to be derived from the Arabic article al and the verb manac, which means to count.

Angular measurements. See Appendix B.

Aphelion. The point where a planet or a comet is farthest away from the sun.

Apparent. To seem real. The daily motion of the Sun round the Earth is only apparent, for we know it is the Earth which turns round on its axis instead.

Arc. See Appendix B.

Arc of circle. See Appendix B.

Aspect. (1) Any curious appearance of an object, especially if the object changes in appearance. (2)The figure formed by a planet with the stars of the constellation which it is in.

Astrologer. One who forecasts the life of a person on the supposition that the stars control it.

Astronomer. One who is skilled in seeing the stars and who knows them.

Atom. A very small particle of matter. See Molecule; Matter.

Attract. To pull toward. The attraction of the Sun and the Earth for each other is due to gravitation.

Attraction. A force which pulls one body to another.

Attraction of Gravitation. A force which pulls all bodies to each other.

Auditory nerve. A nerve that carries the impressions of sound which reach the ear to the brain.

Aurora borealis. The Northern Lights. A glowing light effect which takes place in the Arctic Circle. It can often be seen from our Northern States and sometimes from the Southern States. The same kind of lights appear in the Antarctic Circle. These Southern Lights are called Aurora Australis.

Axes. Plural of axis.

Axis. An imaginary line on which a body turns.

Axis of rotation. An imaginary line round which anything turns or spins.

Axle. A wood or metal rod on which one or more wheels turn, or it may turn with the wheel or wheels.

Badge of merit. A badge awarded by the organization of Boy Scouts to members who can show a certain amount of skill in doing certain things. See Appendix A.

Band. (1) A flat strip of any material, or (2) such a strip whose ends are joined together.

Beam. Rays of light which are parallel. See Ray.

Bearing. (1) A piece of metal, or a bit of agate or other jewel, on which a pivot, spindle or shaft turns. (2) A direction as found by the Sun or stars, or by the compass, sextant or other means.

Body. Any separate and distinct amount of matter when held together. The Sun and Moon are heavenly bodies.

Degree. (1) The 360th part of a circle. (2) Indicated by this sign °.

Device. (1) An apparatus or instrument or any part thereof. Any arrangement for producing a given result.

Diagram. A sort of shorthand picture of an apparatus or part of an apparatus. It is used to show in the simplest and clearest manner the construction of an apparatus.

Diameter. See Appendix B.

Direct line. A straight line.

Disk. (1) A circular plane or flat surface. Since the Sun, Moon and planets seem to be flat their surfaces are called disks. (2) Flat and circular like a coin.

Dog days. So called from the fact that Sirius, the Dog Star, rises at the same time as the Sun.

Ecliptic. See Appendix B.

Elastic. (1) A body that will stretch and return to its original size. (2) A thin piece of rubber.

Ellipse. See Appendix B.

Equator. See Appendix B.

Equatorial. Having to do with or affected by the equator.

Equatorial telescope. A telescope so mounted that its principal axis is parallel with the axis of the earth and moved by clockwork so that it will follow a star.

Evening Star. A planet which can be seen in the west just after the sun sets.

Fixed. (1) Fastened securely. (2) The stars are called fixed because they never seem to change their positions.

Forecast. A prediction of some future event. A forecast may be founded on fancy or on fact. A horoscope of a person is a forecast based on the fancy of an astrologer. A weather forecast is founded on the action of a barometer, and even then the forecast is uncertain enough. Forecasts of the time of eclipses, the return of comets and the like are founded on cold scientific facts and hence come true at exactly the calculated time.

Frequency. How often an event occurs.

Gas. That form of matter which is like air. Some gases remain in the gaseous state at ordinary temperatures. Gases have a tendency to expand without limit. See Vapor.

Generate. To produce. To set up; as a battery generates a current; the Sun generates power.

Gravitation. The force which attracts all bodies near the Earth to it and all bodies to each other.

Heavens. The sky. The space as far as the eye can see about the Earth. The space in which the stars and their planetary systems move.

Horizontal. See Fig. 185.

Horoscope. A forecast of the future of a person made by an astrologer who pretends to read the future from the aspect or position of the planets and stars.

Hyperbola. See Fig. 129.

Hypothesis. See Idea.

Idea. A notion of a plan or scheme which may be more or less vague. Supposition. A clearer conception of a plan or scheme which is based on such facts as may be thought of. Hypothesis. A plan or scheme assumed to be true and carefully reasoned out from all the facts obtainable. Theory. A plan or scheme which has been proved true by experiment, examination or comparison.

Illusion. An image which deceives the eye. The other senses can also be deceived by illusions.

Impact. Coming together of two objects.

Impress. To form on, or to affect, as light waves impress a dry plate.

Indicate. To show. To point out.

Indicator. That which points out or shows something.

Limb. The edge of the Sun, Moon or Planets.

Lore. Learning on any subject.

Lunar. Of, or having to do with the Moon.

Magnetic lines of force. The direction of the force of magnetism acting in and around a magnet.

Magnetic storm. The Earth is a great magnet and sometimes when sun spots of unusual size or numbers appear, the magnetic lines of force of the Earth are violently affected. This is called a magnetic storm.

Mass. (1) Amount of matter. (2) A lot of molecules or particles of matter brought and held together.

Matter. The substance of which a thing is formed. A molecule of matter is made up of atoms, and a mass is a lot of molecules held together by some attractive force.

Mercury. (1) The name of the planet nearest the Sun. (2) A silver white liquid metal.

Molecule. The smallest part of matter that can exist separately without the substance it forms being destroyed.

Morning Star. A planet which can be seen in the east just before the Sun rises.

Morse code. A telegraph code of dots and dashes invented by Samuel F. B. Morse. The Morse Code is used for telegraph and heliograph signaling.

Motion. Anything that changes position. There are two kinds of motion (a) simple motion and (b) compound motion. Simple motion can be either translated or rotary, while compound motion is both translated and rotary, so that while a body is being translated, or moved through space, it is also rotating on its axis. The Sun and planets, then, have compound motions.

Nature. Everything contained in space that has not been shaped by human hands.

Nautical almanac. The American Nautical Almanac is a book of the stars published by the Bureau of Navigation of the United States. It is published three years in advance and is sold by the Superintendent of Documents, Washington, D. C., at 30 cents per copy. This is designed chiefly for the use of navigators of ships. It gives the exact positions of the Sun, Moon and planets and much other astronomical information. It is based upon the calculations made by the United States Naval Observatory; these are printed in the Nautical Almanac, and on this all other almanacs are based.

Northern lights. See Aurora Borealis.

Obscured. Hidden from sight.

Official Handbook of the Boy Scouts. A book published by the organization of Boy Scouts and which contains the rules and regulations of that organization and the requirements they must meet in order to win merit badges.

Offset. To equal; to balance.

Opposition. See Appendix.

Optic Nerve. The nerve that carries the impression of light received by the eye to the brain.

Orbit. The path followed by a body. Atoms have orbits as well as the stars. The paths followed by planets and comets round the Sun.

Parabola. See Fig. 129.

Parallel. See Appendix B.

Particle. A bit of matter. A particle may be a bit of matter which can be seen or it may mean an amount so small that it cannot be seen.

Pencil. A group of rays from the same source of light. See Beam. See Ray.

Pendulum. A body suspended from a fixed point and free to swing.

Perihelion. The point where a planet or a comet is nearest the Sun. As the orbit of a planet is an ellipse and the Sun is in one of the foci—that is near one end—a planet comes nearest to the Sun when at this end of the ellipse; and when the planet is at the other end of its orbit, it is farthest away. See Aphelion.

Period. A certain interval of time which is marked by a repeated occurrence. The period of the Earth round its axis is about 24 hours. Its period around the Sun is 365¼ days.

Periodic. Recurring regularly; as a periodic comet.

Perpendicular. See Appendix B.

Phase. One of the peculiar aspects of a heavenly body; as the phases of the Moon, or the phases of Venus.

Pivot. A pin, spindle or shaft on which a wheel, lever or device rotates or is rotated.

Plane. A level surface, as a table top.

Point. A sharp end. A starting place.

Pores. Minute spaces which separate the molecules of a substance.

Position. The place of a thing when compared to the places of other things.

Precede. To go ahead of. That which is before.

Precession. The act of going ahead or preceding. When a revolving body such as a spinning top or the Earth is acted upon by forces which tend to change the direction of its axis. This change in the direction of its axis is called precessional motion. The pole of the equator of the Earth makes a complete turn round the pole of the ecliptic in a little over 25,000 years and this change in the direction of the axis of the Earth causes the points of the equinox, that is the places where the ecliptic and the equator cross each other to move slowly from west to east and this is termed the precession of the equinoxes.

Prediction. To foretell; to forecast. Predictions may be based on fancy or founded on fact.

Principal. The chief one; the most important.

Principle. The cause of a result. That on which a thing is based.

Process. (1) The way of working. (2) The course of procedure.

Produce. In astronomy the word produce means the lengthening of a line. It is a mathematical term.

Protractor. See Fig. 98.

Quarter circle. See Appendix B.

Ray. (1) A single line of light or heat. (2) The path of light and heat.

Relative position. The position of a thing when compared with the position of something else. See Position.

Revolution. The turning of a thing completely round on its axis.

Revolve. (1) To turn completely round a circle. (2) To turn on an axis, as a top, or the Earth.

Rigid. Firm, that which cannot be easily moved out of its place.

Ring. See Appendix B.

Rise. To come into sight above the horizon, as the Moon rises.

Rotate. To turn completely round on an axis like a top or the Earth.

Rotary. Turning completely round on an axis, like a top or the Earth.

Roughly. Not exactly; nearly enough for practical purposes.

Schedule. (1) A tabulated statement giving items concerning a subject. (2) A timetable of any kind.

Seeing. To look at. The word seeing in starcraft means to observe the stars. Good seeing is to observe the stars when the atmosphere is perfectly clear.

Seems. Something which apparently is true and yet is not necessarily true.

Sensation. The action of one of the senses when excited by some change in matter. Light falling on the retina of the eye produces the sensation of light and color in the brain.

Set. To sink from sight below the horizon; as the Sun sets.

Sight. The power to see. See Sighting.

Sighting. To get the eye and two other objects, such as a telescope and a star, in a line, as to sight Jupiter with a telescope.

Sign. A mark, figure or letter which astronomers have agreed to use to represent certain stars, aspects of stars, parts of the zodiac, etc.

Solar. That which is of, or has to do with the Sun.

Spring stars. The stars which can be seen best during the spring months.

Star chart. A map of the positions of the stars.

Starcraft. Useful knowledge of the stars. Skill shown in making the stars serve useful purposes.

Star finder. A device of any kind which will enable an unskilled person to find the planets or constellations.

Star-lore. Learning concerning the mythology of the stars.

Summer stars. The stars which can best be seen during the summer months.

Supposition. See Idea.

Tangent. See Appendix B.

Tangent line. See Appendix B.

Telegraph code. The alphabet of dots and dashes.

Test. To try out. To examine, compare or make an experiment which will give a needed proof.

Theory. See Idea.

Thumb tack. A short, thin, sharp-pointed tack with a large flat head which permits it to be easily pushed into a board with the thumb. It is used by draftsmen for fastening paper to drawing boards.

Tilting. Leaning from a vertical or plumb line. The axis of the Earth is tilted from the perpendicular 23½ degrees; this throws its equator out of plane with that of the sun, and the circle through the Earth that is in plane with the Sun is called the ecliptic.

Transparent. Said of any substance through which light can pass easily. Anything that may be seen through.

Twinkle. To blink. To flash with varying brightness. The twinkling of stars is caused by the atmosphere.

Uniform. Being the same all through or all along.

Vapor. A gas produced from a liquid or a solid and which returns to its original form at ordinary temperatures. See Gas.

Vertical. See Appendix B.

Vibration. A to-and-fro movement, as the vibration of a particle of matter. A constant to-and-fro movement over the same line.

Visible. That which the eye can see.

Wane. To gradually grow smaller. Said of the Moon.

Wax. To gradually grow larger. Said of the Moon.

Winter Stars. The stars which can best be seen during the winter months.

Wireless Messages. Messages which are sent and received by wireless telegraph stations.

Wireless system. An apparatus for sending and receiving messages by wireless telegraph.

Your meridian. The line running due north and south in the sky directly over your head. A meridian of this kind is called a celestial meridian.

Zodiacal lights. A faint glowing light which may be seen above the western horizon just after twilight during the clear evenings of winter and spring. It can also be seen just before daybreak during the clear mornings of summer and autumn.