An Introduction to AstronomyMacmillan, 1906 - 557 pages |
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Common terms and phrases
altitude amount angle angular apparent motions astronomical atmosphere attraction average axis body bright celestial circle comets computed constellations density depends diameter direction distance diurnal motion earth eccentricity eclipse equal equator equatorial equinox eyepiece fact given greater heat horizon inches inferior planets Jupiter known latitude law of gravitation laws of motion length Lick Observatory light magnitude Mars mass measured Mercury meridian meteors method miles per second moon moon's orbit move nearly nebula Neptune node object observations Observatory parallax pass perihelion perturbations phenomena Photographed photosphere planetoids pole position proper motions radiation radius rays refraction relative respect revolution revolve right ascension ring rotation satellites Saturn seen sidereal period solar system spectroscope spectrum stars sun's superior planets Suppose surface synodic month synodic period telescope temperature theory tion Uranus vary velocity Venus vernal equinox visible Yerkes Observatory
Popular passages
Page 144 - Change of motion is proportional to the impressed force and takes place in the direction of the straight line in which the force acts.
Page 196 - I do not know what I may appear to the world ; but to myself I seem to have been only like a boy playing on the seashore, and diverting myself in now and then finding a smoother pebble or a prettier shell than ordinary, whilst the great ocean of truth lay all undiscovered before me.
Page 460 - While I must leave to others an estimate of the importance of these conclusions, it seems to me that they have a very direct bearing on many, if not all, questions concerning the cosmogony. If, for example, the spiral is the form normally assumed by a contracting nebulous mass, the idea at once suggests itself that the solar system has been evolved from a spiral nebula, while the photographs show that the spiral nebula is not, as a rule, characterized by the simplicity attributed to the contracting...
Page 144 - Every body continues in its state of rest or of uniform motion in a straight line, unless it is compelled to change that state by forces impressed upon it.
Page 460 - They may be briefly summarized as follows: 1. Many thousands of unrecorded nebulae exist in the sky. A conservative estimate places the number within reach of the Crossley reflector at about 120,000. The number of nebulae in our catalogues is but a small fraction of this. 2. These nebulae exhibit all gradations of apparent size, from the great nebula in Andromeda down to an object which is hardly distinguishable from a faint star disk. 3. Most of these nebulas have a spiral structure.
Page 556 - THE MACMILLAN COMPANY 64-66 Fifth Avenue, New York BOSTON CHICAGO SAN FRANCISCO ATLANTA DALLAS...
Page 162 - Each planet revolves so that the line joining it to the sun sweeps over equal areas in equal intervals of time.
Page 175 - ... system is the celestial equator, which is the great circle in which the plane of the earth's equator intersects the celestial sphere. The celestial equator is also called the equinoctial circle, or simply the equinoctial, because, when the sun is in the plane of the equator, the days and nights are of equal length all over the earth. The poles of the equator coincide with the poles of the celestial sphere.
Page 118 - Newton discovered, as a fundamental law of nature, that every particle attracts every other particle with a force which varies directly as the product of the masses and inversely as the square of the distance between them.
Page 126 - This is on the assumption that the diameter of the earth's shadow, at the distance of the moon, is 2^- times the diameter of the moon.