A Compendium of Astronomy |
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altitude angle angular apparent diameter ascertained astronomers atmosphere axis called celestial circle comet constellation degree direction disk distance diurnal diurnal motion earth earth's orbit earth's shadow eccentricity equal equator equinoxes Explain fall figure fixed stars force full moon globe gravity greater greatest elongation heavenly bodies heavens hemisphere Hence Herschel horizon hour inferior conjunction inferior planets Jupiter latitude learner less longitude lunar eclipse magnitude Mercury and Venus meridian miles moon's orbit mountains nearer nearly node oblique observations opposite orbit parallax parallel passing period planetary pole refraction represent respect revolution revolve right ascension ring satellites Saturn seen side sidereal sidereal day solar eclipse sometimes space spectator sphere spots sun and moon sun's light superior planets supposed surface tance telescope tide-wave tides tion transit transits of Mercury transits of Venus tropic Uranus velocity visible west to east Zodiac Zodiacal Light
Popular passages
Page 94 - Newton's Three Laws of Motion," and are as follows: (1) All bodies continue in a state of rest, or of uniform motion in a straight line, unless acted upon by some external force that compels a change.
Page 96 - GRAVITATION, is that influence by which every body in the universe, whether great or small, tends towards every other, with a force which is directly as the quantity of matter, and inversely as the square of the distance.
Page 253 - It was then as bright as Sirius, and continued to increase till it surpassed Jupiter when brightest, and was visible at mid-day. It began to diminish in December of the same year, and in March 1574, had entirely disappeared.
Page 216 - ... of their attraction beyond calculable limits. Under such circumstances, we might have " years of unequal length, and seasons of capricious temperature, planets and moons of portentous size and aspect, glaring and disappearing at uncertain intervals...
Page 114 - A plain, and sometimes a large cavity, is surrounded with a circular ridge of mountains, which encompasses it like a mighty rampart. These annular ridges and plains are of all dimensions, from a mile to forty or fifty miles in diameter, and are to be seen in great numbers over every region of the moon's surface ; they are most conspicuous, however, near the upper and lower limbs, about the time of the half moon.
Page 171 - THIRD LAW. — The squares of the periodical times are as the cubes of the mean distances from the sun. The periodical time of a body is the time it takes to complete its orbit, in its revolution about the sun. Thus the earth's periodic time is one year, and that of the planet Jupiter about twelve years.
Page 252 - This remarkable law of variation certainly appears strongly to suggest the revolution round it of some opaque body, which, when interposed between us and Algol, cuts off a large...
Page 114 - Insulated mountains, which rise from plains nearly level, like a sugar loaf placed on a table, and which may be supposed to present an appearance somewhat similar to Mount Etna or the peak of Teneriffe. The shadows of these mountains, in certain phases of the moon, are as distinctly perceived as the shadow of an upright staff when placed opposite to the sun ; and their heights can be calculated from the length of their shadows. The heights and the length of the base of more than seventy of these...
Page 217 - Place, that the arrangements of the solar system are stable; that, in the long run, the orbits and motions remain unchanged; and that the changes in the orbits, which take place in shorter periods, never transgress certain very moderate limits. Each orbit undergoes deviations on this side and on that side of its average state; but these deviations are never very great, and it finally recovers from them, so that the average is preserved.
Page 218 - ... are periodical and included within narrow limits ; so that the planetary system will only oscillate about a mean state, and will never deviate from it except by a very small quantity. The ellipses of the planets have been, and always will be, nearly circular. The ecliptic will never coincide with the equator, and the entire extent of the variation in its inclination cannot exceed three degrees.