Popular Lectures on Astronomy: Delivered at the Royal Observatory of ParisGreeley & McElrath, 1848 - 95 pages |
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POPULAR LECTURES ON ASTRONOMY Dionysius 1793-1859 Lardner,F. (Francois) 1786-1853 Arago No preview available - 2016 |
Common terms and phrases
angle appear arrived ascer astronomer atmosphere attraction axis body calculation called cause celestial sphere centre Ceres circle circumstances color comet consequently course degrees describe diameter direction disk distance diurnal motion earth ecliptic effect elevated equal equator extreme fact fixed stars Galileo globe gravitation greater grees Halley Halley's comet heat heavens Herschel Hipparchus horizon inclined instrument John Herschel Jupiter latitude lens less luminous magnitude Mars mass Mercury meridian millions of miles month moon moon's motion move nodes object oblique observed orbit parallax pass path perihelion period phenomena planets pole position present produced proportion rays of light reflected refracting telescope refraction revolution right ascension ring rise rotation round the sun satellites Saturn seen shadow sidereal solar space sphere sun's supposed surface tail telescope temperature terrestrial tion traverse Uranus velocity Venus Vesta visible visual magnitude zenith
Popular passages
Page 24 - ... and, calling this a sidereal stratum, an eye placed somewhere within it will see all the stars in the direction of the planes of the stratum projected into a great circle, which will appear lucid on account of the accumulation of the stars; while the rest of the heavens, at the sides, will only seem to be scattered over with constellations, more or less crowded, according to the distance of the planes or number of stars contained in the thickness or sides of the stratum.
Page 5 - ... for their lower parts being nearest to the reflecting surface are seen immediately within it, while their tops seem to hang downward or to extend deeper beyond the surface. CCXXII. When a mirror, C, in the following figure, is inclined forward at an angle of 45 deg. an object AB, if placed in a vertical position, will form a horizontal image ab ; and if the position of the object be horizontal, that of the image will be inverted. Fig. 130. CCXXIII. A person standing before a plane mirror placed...
Page 24 - ... an electric brush issuing from a lucid point ; others of the cometic shape, with a seeming nucleus in the centre, or like cloudy stars, surrounded with a nebulous atmosphere : a different sort again, contain a nebulosity of the milky kind, like that wonderful inexplicable phenomenon about Orionis ; while others shine with a fainter mottled kind of light, which denotes their being resolvable into stars.
Page 24 - ... to the end of the stratum in which he is situated, so that he looks upon these patches as belonging to that system which to him seems to comprehend every celestial object. He now increases his power of vision, and, applying himself to a close observation, finds that the milky way is indeed no other than a collection of very small stars. He perceives that those objects which had been called nebulae are evidently nothing but clusters of stars. He finds their number increase upon him, and when he...
Page 60 - Had the horrid appearance of this body alone been recorded, this description might have passed without the charge of great exaggeration ; but when we find the Great Plague connected with it as a consequence, it is impossible not to conclude that the comet was seen by its historians through the magnifying medium of the calamity which followed it. Another appearance is recorded in the year 1380, unaccompanied by any other circumstance than its mere date.
Page 25 - ... is very regular in its returns, as we found in the year 1714. Since then we have watched, as the absence of the moon and the clearness of the weather would permit, to catch the first beginning of its appearance in a six-foot tube : that bearing a very great aperture discovers most minute stars.
Page 6 - If the medium which the rays enter be denser, they move through it in a direction nearer to the perpendicular drawn to its surface. On the contrary, when light passes out of a denser into a rarer medium', it moves in a direction farther from the perpendicular. This refraction is greater or less ; that is, the rays are more or less bent, or turned aside, from their course, as the second medium, through which they pass, is more or less dense than the first.
Page 24 - ... around him. The whole universe, therefore, to him, will be comprised in a set of constellations, richly ornamented with scattered stars of all sizes. Or if the united brightness of a neighbouring cluster of stars should, in a remarkably clear night, reach his sight, it will put on the appearance of a small, faint, nebulous cloud, not to be perceived without the greatest attention.
Page 65 - Such has been the result of the combination of transcendent mathematical genius and unexampled labor and perseverance for the last century. The learned societies established in the various centres of civilization, have more especially directed their attention to the advancement of physical astronomy: and have stimulated the spirit of inquiry by a succession of prizes offered for the solution of problems arising out of the difficulties which were progressively developed by the advancement of astronomical...
Page 58 - If the path, on the other hand, should appear to be either a parabola or hyperbola, then it would be equally certain that the comet had never been before in our system, and would never return to it. But a difficulty of a peculiar nature obstructs the solution of this question. It so happens that the only part of the course of a comet which can ever be visible, is a portion, throughout which the ellipse, the parabola, and hyperbola so closely resemble one another, that no observations can be obtained...