Popular astronomy. Revised by L. Tomlinson |
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angle Annual variation aphelion apparent diameter appearance ascending node asteroids astronomers attraction celestial celestial sphere centrifugal force changes circle circular clock comet computed conjunction determined direction disc discovered discovery disturbing earth earth's orbit eccentricity ecliptic equal equator exact examination exerted fact fall figure fixed stars globe gravitation heavenly bodies heavens hence Hipparchus hypothesis inclination increase inferior conjunction instruments John Herschel Jupiter Jupiter's Kepler law of Kepler laws of motion light line of nodes longitude lunar magnitude major axis Mars mass Mean distance measure Mercury meridian millions of miles moon moon's orbit nearly observation observatory pass perihelion period of revolution phenomena planet planetary orbits pole position precisely present problem reached retrograde revolution in days revolving ring rotation round satellites Saturn seen Sidereal revolution space sphere spots sun's centre suppose surface telescope tion transit Uranus velocity Venus vernal equinox visible visual ray weight worlds
Popular passages
Page 273 - ... general law. The great eccentricity of the orbits of the comets, is also a result of our hypothesis. If those orbits are elliptic, they are very elongated, since their greater axes are at least equal to the radius of the sphere of activity of the Sun. But these orbits may be hyperbolic ; and if the axes of these...
Page 274 - Such is a summary of the hypothesis of La Place on the origin of the solar system. This hypothesis explains, in the most satisfactory manner, the three most remarkable phenomena presented by the planetary motions. " 1st. The motion of the planets in the same direction, and nearly in the same plane. " 2d. The motion of the satellites in the same direction as their planets.
Page 22 - These planes are inclined to each other, under an angle of 3° 23' 28"-5, one half of the orbit of Venus lying above, or north of the ecliptic, the other half lying below, or south of the ecliptic. The point in which Venus passes from the north to the south side of the ecliptic is called the descending node. She returns from the south to the north of this plane through the ascending node ; and the line joining these two points is called the line of nodes. The transits of Venus, unfortunately for...
Page 78 - In the early part of the evening," he says, "the small bright spot seemed to be partly buried in the large one. After the lapse of an hour or more my attention was again directed to the planet, when I was astonished to find a manifest change in the position of the small bright spot. It had apparently separated from the large spot, and...
Page 170 - In the autumn of the year 1848, the late Professor SC Walker, then of the United States Coast Survey, was engaged with me at the Cincinnati Observatory in a series of observations, having for their object the determination of the difference of longitude between the observatories of Philadelphia and Cincinnati. In comparing our clocks or chronometers with those of Philadelphia, an observer at Philadelphia listening to the clock-beat touched the magnetic key of the...
Page ii - ... proceed to give the following Definitions : — A great circle is one whose plane passes through the centre of the sphere. A small circle is one whose plane does not pass through the centre of the sphere. The axis of the heavens is an imaginary line passing through the centre of the earth, and about which the heavens appear to revolve once in twenty-four hours. A meridian is a great circle passing through the highest point of the celestial sphere (called the zenitfi) and the axis of the heavens.
Page 268 - ... have formed the superior part, and the most condensed the inferior part. If all the nebulous molecules of which these rings are composed, had continued to cool without disuniting, they would have ended by forming a liquid or solid ring. But the regular constitution which all parts of the ring would require for that, and which they would have needed to preserve whilst cooling, would make this phenomenon extremely rare.
Page 269 - ... of change we have just traced in the sun. At first, the condensation of their atmosphere will form round the centre of the planet a body composed of layers of unequal density, the densest matter having, by its weight, approached the centre, and the most volatile reached the surface, as we see in...
Page 268 - ... at the same time, in consequence of their separation, they would acquire a rotatory motion round their respective centres of gravity ; and as the molecules of the superior part of the ring— that is to say, those farthest from the centre of the sun — had necessarily an absolute velocity greater than the molecules of the inferior part which is nearest it, the rotatory motion common to all the fragments must always have been in the same direction with the orbitual motion.
Page 203 - ... exhibition of the reasoning which was employed to narrow the limits of research in the effort to point the telescope to the unknown cause of the perturbations of Uranus. No account, of course, can be given of the mathematical treatment of the problem. It was undertaken at about the same time by Adams, of England, and by Le 'Verrier, of Paris. Each computer, unknown to the other, reached a result almost identical. Le Verrier communicated his solution to the Academy of Sciences on the 31st August,...