Discarding those of Uranus, in which the orbits of the satellites are highly inclined to the ecliptic, and in which manifestly some exceptional influences have been at work, we find that the satellites revolve around the primaries also in the same direction (Exceptions are Saturn ix.
Eratosthenes (276-196 B.C.) used most probably a solstitial armilla for measuring the obliquity of the ecliptic. Hipparchus (160-125 B.C.) probably used an armillary sphere of four rings.
In the astral theology of Babylonia and Assyria, Anu, Bel and Ea became the three zones of the ecliptic, the northern, middle and southern zone respectively.
One of these is the position of the line MN through the sun at F in which the plane of the orbit cuts some fundamental plane of reference, commonly the ecliptic. This is called the line of nodes, and its position is specified by the angle which it makes with some fixed line FX in the fundamental plane.
Trepidare, to tremble), a term meaning, in general, fear or trembling, but used technically in astronomy for an imagined slow oscillation of the ecliptic, having a period of 7000 years, introduced by the Arabian astronomers to explain a supposed variation in the precession of the equinoxes.
The orbital planes of earth and moon are inclined to each other at an angle of 50.8 ° and at two points only in its orbit can the moon be situated in the plane of the ecliptic: the line joining these two points is called the "line of nodes."
Each discovery in turn was, according to the prevailing custom, announced to the learned world under the veil of an anagram - removed, in the case of the first, by the publication, early in 1656, of the little tract De Saturni luna observatio nova; but retained, as regards the second, until 1659, when in the Systema Saturnium the varying appearances of the so-called "triple planet" were clearly explained as the phases of a ring inclined at an angle of 28° to the ecliptic. Huygens was also in 1656 the first effective observer of the Orion nebula; he delineated the bright region still known by his name, and detected the multiple character of its nuclear star.
Its weak point is that the apparent motion of the node depends partly upon the motion of the ecliptic, which cannot be determined with equal precision.
The great variety in the apparent motions of meteors proves that they are not directed from the plane of the ecliptic; hence their orbits are not like the orbits of planets and short-period comets, which are little inclined, but like the orbits of parabolic comets, which often have great inclinations.
In astronomy, the longitude of a celestial body is the distance of its projection upon the ecliptic from the vernal equinox, counted in the direction west to east from o° to 360°.
It is bounded by two circles equidistant from the ecliptic, about eighteen degrees apart; and it is divided into twelve signs, and marked by twelve constellations.
These were called by the Greeks " decans," because ten degrees of the ecliptic and ten days of the year were presided over by each.
2 Projected upon the ecliptic, these were considerably unequal, and the tse accordingly differed essentially from the Chaldaean and Greek signs.
Its invocation with the other nakshatras, remoteness from the ecliptic notwithstanding, was thus due (according to Max Miiller's plausible conjecture)' to its being regarded as of especially good omen.
Here the " signs " and the " constellations " of the lunar zodiac form two essentially distinct systems. The ecliptic is divided into twenty-seven equal parts, called bhogas or arcs, of Boo' each.
They were called the " media of the whole circle of the zodiac "; 11 each ten-day period of the Egyptian year was consecrated to the decanal god whose section of the ecliptic rose at its commencement; the body was correspondingly apportioned, and disease was cured by invoking the zodiacal regent of the part affected.
Among his happy conjectures may be mentioned that of the sun's axial rotation, postulated by him as the physical cause of the revolutions of the planets, and soon after confirmed by the discovery of sun-spots; the suggestion of a periodical variation in the obliquity of the ecliptic; and the explanation as a solar atmospheric effect of the radiance observed to surround the totally eclipsed sun.
The chief conclusions of astronomers concerning the .spherical figure and dimensions of the earth, its relation to the heavenly bodies, and the great circles of the globe - the equator, the ecliptic and the tropics - were considered as well established.
The Solar Astronomical Year Is The Period Of Time In Which The Earth Performs A Revolution In Its Orbit About The Sun, Or Passes From Any Point Of The Ecliptic To The Same Point Again; And Consists Of 365 Days 5 Hours 48 Min.
Each solstice is upon the ecliptic midway between the equinoxes, and therefore go from each.
The ecliptic, and since it is equal to the ratio of the velocity of light to the velocity of the earth, it is necessarily constant.
The "ways" appear in this instance to have been the designation of the ecliptic circle, which was divided into three sections or zones - a northern, a middle and a southern zone, Anu being assigned to the first, Bel to the second, and Ea to the third zone.
Jacques Cassini also proved that Arcturus had even since the time of Tycho Brahe shifted five minutes in latitude; for r l Bootis, which would have shared in the change, if it had been due to a motion of the ecliptic, had not moved appreciably.
Since the sun moves in the ecliptic, it is in the last-named sense the point of intersection of the ecliptic and the celestial equator.
He taught, if he did not discover, the obliquity of the ecliptic, is said to have introduced into Greece the gnomon (for determining the solstices) and the sundial, and to have invented some kind of geographical map. But his reputation is due mainly to his work on nature, few words of which remain.
ECLIPTIC, in astronomy.
The plane of the ecliptic is that plane in or near which the centre of gravity of the earth and moon.
The ecliptic itself is the great circle in which this plane meets the celestial sphere.
Owing to the action of the moon on the earth, as it performs its monthly revolution in an orbit slightly inclined to the ecliptic, the centre of the earth itself deviates from the plane of the ecliptic in a period equal to that of the nodal revolution of the moon.
Owing to the action of the planets, especially Venus and Jupiter, on the earth, the centre of gravity of the earth and moon deviates by a yet minuter amount, generally one or two tenths of a second, from the plane of the ecliptic proper.
Owing to the action of the planets, the position of the ecliptic is subject to a slow secular variation amounting, during our time, to nearly 47" per century.
The obliquity of the ecliptic is the angle which its plane makes with that of the equator.
The motion of the ecliptic produces a secular variation in the obliquity which is now diminishing by an amount nearly equal to the entire motion of the ecliptic itself.
The laws of motion of the ecliptic and equator are stated in the article Precession Of The Equinoxes.
Attempts have been made by Laplace and his successors to fix certain limits within which the obliquity of the ecliptic shall always be confined.
The formula for the obliquity of the ecliptic, as derived from the laws of motion of it and of the equator, may be developed in a series.
Finally there is the envelope of still vaster extent and of unknown constitution which gives the zodiacal light; its greatest extent is along the ecliptic, but it can also be certainly traced for 35° in a perpendicular direction.
Equator; inclination to ecliptic: 7° 15'.