Orbit

“ And if we are swept, as it were, out of the little orbit that we move in, when the latter is our centre, and are drawn by the weight and mass of the great central sun to become its satellites, then we move in a nobler orbit and receive fuller and more blessed light and warmth. ”

“ Such an orbit must appear practically as a straight line, with the sun at its middle point, and along this line the planet will appear to travel like a bead on a wire, appearing now on one side of the sun, now on another. ”

“ Now, the length of a planet's orbit is subject only to these very small oscillations, and it may therefore be regarded as fixed or constant. The breadth of the orbit, however, is subject to secular variations, which require ages for their full compensation. The orbit alternately bulges out into a circle, and narrows into an ellipse. The earth is now, and has been for many ages, expanding into a circle, but it will again collapse into an ellipse. ”

“ The summation of the whole matter is that the orbit in which a body moves around the sun, or past the sun, depends upon its velocity and if this velocity and the direction of the motion at any one point in the orbit are known the whole orbit is determined by them, and the position of the planet in its orbit for past as well as future times can be determined through the application of Newton's laws; and the same is true for any other heavenly body—moon, comet, meteor, etc. ”

“ When we contemplate, for example, the globe on which we stand—think of it as moving at the rate of more than sixty thousand miles per hour, around that luminous orb, which at the distance of millions of miles, binds it down to its prescribed orbit ”

“ The orbits of the planets change not only their position, but even their magnitude and their form: the longer axis of each has a slow angular motion; and, though its length remains fixed, the shorter axis increases and diminishes, so that the form of the orbit approaches to that of a circle, and recedes from it by turns. ”

“ Motion of the perihelion of the terrestrial orbit.—The major axis of the orbit of each planet is in a state of continual movement from the disturbing action of the other planets. In some cases, it makes the complete tour of the heavens; in others, it merely oscillates around a mean position. In the case of the earth's orbit, the perihelion is slowly advancing in the same direction as that in which all the planets are revolving around the sun. ”

“ The large arrows show the direction in which the planet travels in its revolution about the sun, and the small curved arrows the direction in which it rotates on its axis. Now, in moving along its orbit from A to B the planet, partly because of its swifter motion when near the sun, and partly because of the elliptical nature of the orbit, traverses a greater angular interval with reference to the sun than the cross, moving with the uniform rotation of the planet on its axis, is able to traverse in the same time. ”

“ And thus it would be if the moon was uniformly revolved in a circular orbit. But if the orbit is elliptical, the mean motion of the nodes will be diminished in proportion of the lesser axis to the greater, as we have shewn above; and the variation of the inclination will be also diminished in the same proportion. ”

“ When a planet is knocked out of the outer ring (the orbit of Herschel) , it belongs to him who strikes it out: the loser must replace it by putting a marble down in its original place.
11. When a planet is struck within the orbit of any other planet, the player striking it there has to pay him [Pg 18] to whom the orbit belongs, as many marbles as there are satellites.
12. Should a player's taw, after it has struck another taw, a planet, or a satellite, fall into its own orbit, he has to put one in the inner ring as stakes for the winner of the game. ”

“ Eccentricity of Orbit of Moon.--From astronomical observation we learn, that all the satellites and planets do not possess uniformity of motion, as they are carried round their controlling centres by the circulating aetherial currents, because the respective controlling centres themselves move through space. The result is, that the orbit of any satellite or planet is not always of the same size, but constantly varies, sometimes having a larger circumference than at other times, and sometimes a smaller circumference. ”

“ That part of the force which is in the direction NM, perpendicular to the orbit, produces an effect similar to that which gravity produces in the motion of a cannon ball : it makes the orbit curved. But that part which acts in the direction of OM, parallel to the orbit, produces a different effect; it accelerates the planet's motion in its orbit. Thus, in going from l towards L, the planet is made to go quicker and quicker. ”

“ If the orbit were a circle it is evident at a glance that the law must be true, because then the sun would be situated in the centre of the circle, the length of the radius vector, no matter where the planet might be in the orbit, would never vary, and the area swept over by it in one day would be equal to the area swept over in any other day, because all these areas would be precisely similar and equal triangles. ”

“ We modestly lay claim to this small corner of the universe, denominated the solar system, and assert our right to possession by calling it ours. What is the area of this plane bounded by Neptune's orbit, with which the planes of the other planetary orbits nearly coincide? What is the space swept by the radius-vector of this planetary child of Adams's and Le Verrier's calculations? Since circles are as the squares of their radii, this area is 900 times that comprised within the earth's orbit. ”

“ Now, if we suppose our sun-bearing wheel to turn so slowly that the sun revolves but once about its imaginary hub while the wheel itself is making the entire circuit of the orbit, we shall have accounted for the observed fact that the sun passes more quickly through one-half of the orbit than through the other. ”

“ That the speed of planetary motion varies in different parts of the orbit in such a way that an imaginary line drawn from the sun to the planet—that is to say, the radius vector of the planet's orbit—always sweeps the same area in a given time. ”

“ If we take the plane of our earth’s orbit, which we call the ecliptic, as the standard, then the greatest inclination of the orbit of any other important planet is seven degrees, which is found in the case of Mercury. ”

“ Not only is the orbit of a planet round the sun elliptic in form, but the path of the moon round the earth, or the path of any satellite, as for example a satellite of Mars or Jupiter or Saturn, is also that of an ellipse, the planet round which it revolves occupying one of the Foci. ”

“ Look at it how we will, we seem to be conducted to the conclusion that the ring is really an enormous shoal of extremely minute bodies; each of these little bodies pursues an orbit of its own around the planet, and is, in fact, merely a satellite. These bodies are so numerous and so close together that they seem to us to be continuous, and they may be very minute—perhaps not larger than the globules of water found in an ordinary cloud over the surface of the [Pg 287] earth, which, even at a short distance, seems like a continuous body. ”

“ Or if, according to the much more probable theory, the heavens are fluid, and every star describes an orbit of its own, according to what law then, or for what reason, are their orbits so arranged that, when looked at from the earth, they appear to be contained in one single sphere? ”

“ If each star is moving in some orbit, the orbit is so immense that no curvature can be perceived in the short arc which has been described since accurate determinations of the position of the stars began to be made. * * * The stars in all parts of the heavens move in all directions, with all sorts of velocities. It is true that by averaging the proper motions, as it were, we can trace a certain law in them; but this law indicates, not a particular kind of orbit, but only an apparent proper motion, common to all the stars, which is probably due to a real motion of our sun and solar system. ”

“ The commencement and end of the orbit, where the motion should be in the same direction as the body, is most difficult to observe, though even this detail is visible if the orbit selected be sufficiently near to the axis of flight. ”

“ Above all these spheres, a primum mobile gave motion to the whole machine, making it turn from east to west, but each planet and each fixed star made an effort against this motion, by means of which each of them accomplished their revolution about the earth in greater or less time, according to its distance, or the magnitude of the orbit it had to accomplish. ”

“ In leafage they mark the forces of its growth and expansion, but some among the most beautiful of them are described by bodies variously in motion, or subjected to force; as by projectiles in the air, by the particles of water in a gentle current, by planets in motion in an orbit, by their satellites, if the actual path of the satellite in space be considered instead of its relation to the planet ”

“ Since his capsule, like all heavenly bodies, was stable in position with respect to the entire universe and, thanks to Sir Isaac Newton and his laws, never changed, the Earth and the stars alternated over his head during each orbit. ”

“ Again, the motion of a planet is a progressive effect, produced by causes at once permanent and progressive. The orbit of a planet is determined (omitting perturbations) by two causes: first, the action of the central body, a permanent cause, which alternately increases and diminishes as the planet draws nearer to or goes farther from its perihelion, and which acts at every point in a different direction; and, secondly, the tendency of the planet to continue moving in the direction and with the velocity which it has already acquired. ”