An Elementary Treatise on Astronomy: Adapted to the Present Improved State of the Science : Being the Fourth Part of a Course of Natural Philosophy, Compiled for the Use of the Students of the University at Cambridge, New England |
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Common terms and phrases
altitude angle apogee apparent diameter Astron astronomers atmosphere axis of rotation calculate called celestial sphere centre circle circle of latitude comets consequently considered declination deduced described determine diminish direction disc diurnal motion earth ecliptic effect epoch equal equator equinoctial point exactly formulas greatest heavenly bodies heavens horary horizon horizontal parallax inequalities instant interval Jupiter latitude laws light luminous lunar manner mean distance mean longitude mean motion meridian moon moon's nearly node nutation obliquity observations obtain opposite orbit parallax parallel passes perigee period perpendicular phenomena plane pole position preceding precession proper motion quantity ratio reckoned refraction respect retrograde revolution right ascension satellites Saturn seen semidiameter shadow sidereal sidereal day sine situated solar solstice spherical stars straight line sun's suppose supposition surface take place tang telescope terrestrial tion transits triangle tropical true variations velocity Venus vernal equinox vertical visual ray zenith distance
Popular passages
Page 395 - Thus a yellow colour predominating in the light of the brighter star, that of the less bright one in the same field of view will appear blue ; while, if the tint of the brighter star verge to crimson, that of the other will exhibit a tendency to green — or even appear as a vivid green, under favourable circumstances.
Page 395 - In such instances, the larger star is usually of a ruddy or orange hue, while the smaller one appears blue or green, probably in virtue of that general law of optics, which provides, that when the retina is under the influence of excitement by any...
Page 316 - That feelings of awe and astonishment should be excited by the sudden and unexpected appearance of a great comet, is no way surprising ; being, in fact, according to the accounts we have of such events, one of the most brilliant and imposing of all natural phenomena.
Page 319 - ... objects, with little or no tail; but by degrees accelerate, enlarge, and throw out from them this appendage, which increases in length and brightness till (as always happens in such cases) they approach the sun, and are lost in his beams. After a time they again emerge, on the other side, receding from the sun with a velocity at first rapid, but gradually decaying. It is for the most part after thus passing the sun, that...
Page 317 - BC, that it occupied a third of the hemisphere, or 60° ; that of AD 1618, is stated to have been attended by a train no less than 104° in length. The comet of 1680, the most celebrated of modern times, and on many accounts, the most remarkable of all, with a head not exceeding in brightness a star of the second magnitude, covered with its tail an extent of more than 70° of the heavens, or, as some accounts state, 90°...
Page 395 - ... a red and a green, or a yellow and a blue one — must afford a planet circulating about either; and what charming contrasts and "grateful vicissitudes," — a red and a green day, for instance, alternating with a white one and with darkness, — might arise from the presence or absence of one or other, or both, above the horizon.
Page 383 - Sirius cannot be so small as 200000 times that of the sun. Hence it follows, that, upon the lowest possible computation, the light really thrown out by Sirius cannot be so little as double that emitted by the sun ; or that Sirius must, in point of intrinsic splendour, be at least equal to two suns, and is in all probability vastly greater...
Page 380 - Herschel, whose powerful telescopes have effected a complete analysis of this wonderful zone, and demonstrated the fact of its entirely consisting of stars. So crowded are they in some parts of it, that by counting the stars in a single field of his telescope, he was led to conclude that 50,000 had passed under his review in a zone two degrees in breadth, during a single hour's observation.
Page 386 - Venus, and disappearing entirely. In the years 945, 1264, and 1572, brilliant stars appeared in the region of the heavens between Cepheus and Cassiopeia; and, from the imperfect account we have of the places of the two earlier, as compared with that of the last, which was well determined, as well as from the tolerably near coincidence of the intervals of their appearance, we may suspect them, with Goodricke, to be one and the same star, with a period of 312 or perhaps of 156 years.
Page 402 - Resolvable nebulae can, of course, only be considered as clusters either too remote, or consisting of stars intrinsically too faint to affect us by their individual light, unless where two or three happen to be close enough to make a joint impression, and give the idea of a point brighter than the rest. They are almost universally round or oval — their loose appendages, and irregularities of form, being as it were extinguished by the distance, and the only general figure of the more condensed parts...