Orbit of Earth

“ 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. ”

“ The Earth accomplishes a revolution of her orbit in 365 days 6 hours 9 minutes; in her journey round the Sun she travels a circuit of 580,000,000 miles at an average pace of 66,000 miles an hour. The Earth has other slight motions called perturbations, which are produced by the gravitational attraction of other members of the solar system. The most important of these is Precession of the Equinoxes, which is caused by the attraction of the Sun, Moon, and planets, on the protuberant equatorial region of the globe. ”

“ According to the best tables we now have, the planes of the orbits of Jupiter, the Earth and Mercury are immoveable, though the orbits themselves have a progressive motion in their planes. On the contrary, the poles of the orbits of Saturn, Mars and Venus are supposed to revolve about the poles of the earth’s orbit, with such velocities as at present nearly reconcile calculation to appearances. ”

“ Answer.—The earth’s orbit is not a perfect circle, but an ellipse with the sun in one of the foci, at a point on the long diameter of the orbit something more than a million miles from the center in the direction of perigee, or the place where the earth approaches nearest to the sun. ”

“ The radius of the orbit in which those bodies travel is sixty-five times the distance of the Earth from the Sun; which means that they travel in an orbit twice the width of that of the planet Neptune. It has been estimated that they complete a revolution in about eight centuries. The united mass of the system is about one-half that of the Sun, and in point of luminosity they are much inferior to that orb. ”

“ The effect of the constantly widening orbit would be much as if the whole motion took place on one midway between those of the Earth and Mars, say 120 millions of miles from the Sun. The arc described on this orbit would be equivalent to 86 millions of miles on that of Mars. The entire arc of his orbit between the point opposite to that occupied by the Earth when I started and the point of opposition—the entire distance I had to gain as measured along his path—was about 116 millions of miles ”

“ 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. ”

“ 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. ”

“ 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. ”

“ That is, taking 95,000,000 of English miles as the mean radius of the Earth’s orbit, we have 95 × 1·623 = 154·185 millions of miles; and consequently,
The Sun and all his planets, primary and secondary, are therefore now in rapid motion round an invisible focus. To that now dark and mysterious centre, from which no ray, however feeble, shines, we may in another age point our telescopes, detecting perchance the great luminary which controls our system and bounds its path: into that vast orbit man, during the whole cycle of his race, may never be allowed to round.—North-British Review, No. ”

“ 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. ”

“ The orbit in which our earth revolves is much more nearly circular than is the orbit of Mars, but still the variations of the distance between the earth and the sun are too large to be overlooked, even though they may seem relatively unimportant. Under certain circumstances our earth may be as far from the sun as 93,500,000 miles, while the smallest magnitude to which the distance can shrink is 90,500,000 miles. ”

“ Now, in the case of meteors which are really traveling in the large orbit, this shifting of the orbit must be due to the attraction of the planets Jupiter, Saturn, Uranus, and the Earth, while, if they had traveled in any of the four smaller orbits, the planets that would be near enough and large enough to act sensibly upon them would be the Earth, Venus, and Jupiter. ”

“ Uranus travels through space in an orbit at an average distance of 1,771,000,000 miles from the sun, encompassing the orbits of Saturn, Jupiter, the Planetoids, Mars, Earth, Venus and Mercury; an orbit so large that it takes the planet 84 years to complete its journey around the sun. ”

“ The dimensions of a planetary orbit are so stupendous that the planet must run its course very rapidly in order to finish the journey within the allotted time. The earth, as we have already seen, has to move eighteen miles a second to accomplish one of its voyages round the sun in the lapse of 365-1⁄4 days. ”

“ After that the eccentricity of the earth's orbit will begin to increase, and will continue to increase for about 40,000 years, according to some scientists, which implies that the sun will then have started from its aphelion point, so to speak, and will begin its return journey towards its central body, gradually getting nearer and nearer. As it gets nearer its orbital velocity will be proportionately increased, with the result that the eccentricity of the earth's orbit will increase also. ”

“ It is easy to see that with a circular orbit and with an inclined axis winter and summer would normally come always at the same point in the orbit, and that these seasons would be of perfectly even length. But, as we have before noted, the earth's path around the sun is in its form greatly affected by the attractions which are exercised by the neighbouring planets, principally by those great spheres which lie in the realm without its orbit, Jupiter and Saturn. ”

“ The fields will be constantly moving. Fixed in an orbit 25,000 miles above the Earth a space-mine would always remain over the same Earthly spot and there is a similar critical distance for the Moon, Mars, and the asteroids. ”

“ In the first place, we must note that the ellipticity of the earth's orbit is not developed on fixed lines, but is endlessly varied, as we can readily imagine it would be for the reason that its form depends upon the wandering of the outer planetary spheres which pull the earth about. ”

“ But the earth's orbit is not always the same; there have been periods when the orbit described resulted in a considerably greater difference than three million miles, and it is thought that if this ordinary eccentricity of the orbit is insufficient to account for the Glacial epoch, the periods of greater eccentricity would. ”

“ 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. ”