Eccentricity (astronomy)

“ But this eccentricity is steadily diminishing at a uniform rate, by reason of the perturbing influence of the other planets. In the case of some other planets it is steadily increasing, and, if it were to go on a sufficient time, might cause frightful extremes of temperature ”

“ The motion of the planets themselves through the medium in nearly circular orbits would concur in imparting to it a revolution in the same direction. Whether, therefore, we receive or reject the nebular hypothesis, the resistance of the ethereal medium to bodies moving in orbits of small eccentricity and78 in the direction of the sun's rotation, becomes an infinitesimal quantity.
The hypothesis of Encke, it is well known, was based solely on the observed acceleration of the comet which bears his name. ”

“ He found it at last in the eccentricity of the earth’s orbit. This world of ours, though usually steady enough in its movements, is at times decidedly eccentric. Not that I mean to impute to our old and exceedingly respectable planet any occasional aberrations of intellect, or still less of morals (such as might be expected from Mars and Venus) ”

“ In this way it comes about that some periods of high eccentricity have lasted much longer than others, and that the orbit has been more elliptical at some epochs of high eccentricity than at others.”14 We have just seen that the earth is nearer the sun at one time of the year than at another. ”

“ A phenomenon not only very difficult to explain under this hypothesis, but one which is even contrary to it, is the slight eccentricity of the planetary orbits. We know, by the theory of central forces, that if a body moves in a closed orbit around the sun and touches it, it also always comes back to that point at every revolution; whence it follows that if the planets were originally detached from the sun, they would touch it at each return towards it, and their orbits, far from being circular, would be very eccentric. ”

“ To suppose them independent planets, as they must necessarily be if they did not originally form one, their diminutive size, the great eccentricity and inclination of their orbits, and their numerous intersections, when projected on the plane of the ecliptic, are phenomena absolutely inexplicable on every principle of science, and subversive of that harmony and order which before the discovery of these bodies, seemed to pervade the planetary system. ”

“ Even the extreme eccentricity of some of their orbits, and the large tilt of some of them to the ecliptic, may be suggestive in finally solving certain planetary problems, for these impish little bodies are far from conforming to the regular ways of the planets, and there is, of course, some mechanical reason for their apparent waywardness. ”

“ We should have no guarantee that the eccentricities would for ever remain small, as they are at present. In a similar manner, the planets all move in orbits whose planes are inclined to each other at very small angles. The positions of those planes fluctuate, but these fluctuations are confined within very narrow limits. The proof of this theorem, like the proof of the corresponding theorem about the eccentricities, depends upon the actual conditions of the planetary system as we find it. ”

“ Can the attraction of any foreign body change a rotatory motion into a libratory one, and a libratory motion into rest, in spaces so very free from all resistance as those wherein the planets move? There are other defects in Astronomy that are purely optical. Removing of those, depends on the further improvement of telescopes, or rather on the more judicious use of them, at times and places the most favourable. ”

“ But with the stars themselves all in motion at various speeds and in many directions, the changes occur more rapidly. Of course, “rapid” is here understood in a relative sense; the wheel of human history to an eye accustomed to the majestic progression of the universe would appear to revolve with the velocity of a whirling dynamo. Only the deliberation of geological movements can be contrasted with the evolution and devolution of the constellations.
And yet this secular fluctuation of the constellation figures is not without keen interest for the meditative observer. ”

“ The most wonderful thing about it is the inclination of its orbit--thirty-five degrees--to the plane of the ecliptic; which means that at each revolution in its orbit, it swings that much above and below the imaginary plane cutting the sun at its equator, from which the earth and other larger planets vary but little. This no doubt is due to the near approach and disturbing attraction of some large comet, or else it was flung above or below the ordinary plane in the catastrophe that we think befell the large planet that doubtless formerly existed where we now find this swarm. ”

“ And yet, is not the saying a witness to the presence in that wondrous and gentle career of an element entirely unlike what exists in the most of mankind? Here was a new star in the heavens, and the law of its orbit was manifestly different from that of all the rest. That is what 'eccentric' means—that the life to which it applies does not move round the same centre as do the other satellites, but has a path of its own. ”

“ We know that over vast periods of time a sun's rotatory speed will increase, due to the slow shrinkage of its mass, and that when the speed has increased to a point where its centrifugal force is greater than its own power of cohesion, the sun breaks up like a bursting flywheel, breaks up or divides into a double or multiple star. Thousands upon tens of thousands of the stars of our universe are double or multiple stars, having been formed thus from dividing single suns, whose speed or rotation became too great. ”

“ Suppose that we could see the huge planets and the ponderous stars whirling their terrific masses with awful, and if it might be so, clamorous velocity, and thundering through the fields of unresisting space with furious gigantic momentum, such as the mighty avalanche most feebly figures, and thus describing with chafing eccentricities and frightful deflections, their mighty centre-seeking and centre-flying circles, we should behold in the nakedness of its tremendous operations the Divine law of gravitation. ”

“ The glorious rush together of the star-children through the vast abysses, drinking up the energy of the radiation about them. The audacious and dangerous coasting along the shores of dark nebulae, racing the lumbering comets and leaving them behind, on until you felt through all your photons the beckoning warmth of the star you approached. Ignore the cinders called planets that creep around it, speed faster, faster, brothers, the way has been long but we are almost there! ”

“ It is slowly distorted by the attractions of the other planets, for ages it may be nearly circular, for ages it is more or less elliptical. As the ellipse becomes most nearly circular, then the focus becomes most nearly the centre. When the orbit becomes most elliptical, then the position of the sun becomes most remote from the middle or, to use the astronomer’s phrase, most eccentric. ”