Obeying Signs. v. Signs.

 

Oblique Ascendant. v. Ascensional Difference.

 

Oblique Ascension. (O.A.) As it rises, a star or planet, not on the equator, forms an angle with that part of the equator which is rising at the same time. This is called its Ascensional difference. (A.D.) This A.D. added to the R.A. if it have S. declination, and subtracted therefrom if it have N. declination, gives its Oblique Ascension. In the Southern hemisphere, reverse; add, if N.; subtract, if S.

 

The equator is always at right angles to a line between the North and South Poles. Any meridian circle can be considered as the horizon of a place on the equator go degrees distant from that meridian - hence, from that point such meridian can be called the horizon of the pole.

 

At either pole a planet on any parallel of declination moves along an arc parallel to the equator, to the horizon of the pole. It has neither ascension nor descension, but remains, day and night, above or below the horizon, according as it is in North or South declination. Viewed from a place on the equator, a star will by the axial rotation of the Earth, be carried along an arc parallel to the equator: hence it rises and sets at right angles to the horizon of that place. All places in latitudes north and south of the equator, have a prime vertical that cuts the equator at an angle equal to the latitude of the place; and the horizon cuts the equator at an angle equal to the complement of the latitude. Stars and planets rise and set obliquely, since they follow arcs parallel to the equator - to which the horizon is oblique. The semi-arc of a body on the equator is always go degrees, or 6 hours; the whole arc is always 180 degrees or 12 hours. On the equator days and nights are equal, and the semi-arcs of all bodies are equal; but in latitudes north or south of the equator the arcs above and below the horizon are unequal, although together these make 180 degrees or 12 hours. The difference between 90 degrees and the diurnal or nocturnal semi-arc of a body is thus its Ascensional Difference; and its Right Ascension, plus or minus this Ascensional Difference, is its Oblique Ascension.

 

Oblique Descension. The complement of Oblique Ascension: 180 degrees, minus the Oblique Ascension, equals the Oblique Descension.

 

Oblique Sphere. Any sphere that is not in the same vertical as the poles of the Earth. All circles parallel to the equator arc oblique to the horizon - caused by the depression of the pole of the place from the Pole of the Earth. All places located between the poles and the equator are in an oblique sphere.

 

Occidental or Oriental. These terms have various meanings, when differently applied; as: (1) The Moon is oriental of the Sun when it is increasing in light, from the lunation to the full; occidental of the Sun, when decreasing in light. (2) A planet is said to be oriental of the Sun when it rises and sets before the Sun; occidental of the Sun, when it rises and sets after the Sun. Planets are said to be stronger when oriental of the Sun and occidental of the Moon. (3) Applied to the Sun, a special significance is involved in that when the Sun is setting in one hemisphere it is rising in the other. Therefore the Sun is said to be oriental in Houses 12, 11, 10, 6, 5, or 4; and occidental in the opposite Houses. Thus the oriental Houses arc those which have passed the horizon and are culminating toward the meridian; the occidental Houses, those which have passed the meridian and are moving toward the horizon. Some authorities speak of the Eastern Houses, the entire eastern half of the Figure, as the oriental Houses; the entire Western half, as the occidental Houses. This practice only introduces confusion and should be discouraged. If one must use the term, it should always be qualified; either as "in an oriental House" or "oriental of the Sun." The same applies to Occidental. v. Orientality.

 

Occultation. When a planet or star is hidden or eclipsed by another body, particularly by the Moon, there results what is termed an occultation.

 

Occursions. Celestial occurrences; such as, ingresses, formation of aspects, and conjunctions.

 

Occursor. A term applied by Ptolemy to the planet which moves to produce an occursion. Now generally superseded by Promittor.

 

Old Style. v. Calendar.

 

Opposition. v. Aspects.

 

Omniverse. A technical article applied the word to all creation in all space, as distinguished from "universe," designating all creation in our solar system. As the solar system is entirely under the domination of the Milky Way galaxy of which it is a unit, the term universe should embrace the whole of the galaxy, and omniverse the galaxy of galaxies that embraces all known and unknown stars and star-clusters.

 

Orbit. The path described by a heavenly body in its revolution around a center of attraction. Since the attracting mass is also in motion, the orbit must necessarily be an ellipse. The position of the center of the attracting mass is the focus of the ellipse. The line from the focus to any point of the orbit is the radius vector. If the plane of the orbit intersects any other plane, the two points of intersection are the nodes. The nearest point to the center is the peri-center, or lower apsis (the smallest-distance); the most distant point, the apocenter, or higher apsis. As indicating the particular attracting center involved, the pericenter becomes perihelion (helio, the Sun) to a body revolving around the Sun; and perigee (geo, the Earth), around the Earth. Thus, according to Kepler's law that "the radius vector sweeps over equal areas (arcs) in equal times," as the body approaches the pericenter, its motion is accelerated; as it recedes, the motion is retarded. These points are collectively termed Apsides: the diameter running through the Line of Apses. Aphelion. The point at which any planet, including the Earth, is at its greatest distance from the Sun, the apo-center of its orbit. Perihelion. At the closest point to the Sun. Apogee. Said of the Moon, when at its greatest distance from the Earth. Perigee. At the closest point to the Earth.

 

The so-called six Elements of an orbit are: eccentricity; mean radius vector; inclination of its orbit plane to that of the Ecliptic; longitude of its ascending node; period of revolution; and time of passage across a given point, such as perihelion.

 

Orbital revolution. The annual motion of the Earth in an elliptical orbit round the Sun. Applicable also to the motion of any celestial body which pursues an orbit around any other body.

 

Oriental. v. Occidental.

 

Orbs. The space within which an aspect is judged to be effective. The term is employed to describe the arc between the point at which a platic, or wide aspect, is deemed strong enough to be operative, and the point of culmination of a partile or exact aspect. Most authorities agree that orbs should vary with each planet and aspect, and that a larger orb should be allowed for an aspect that is forming than for one that is separating. As to exact orbs, there are few points on which authorities differ so radically. For conjunction or opposition some allow as much as 12° when the Sun aspects the Moon, about 10° when either luminary aspects a planet, and 8° for aspects between planets. Observe whether either body is in retrograde motion. The faster moving applies to the slower.

 

According to Ptolemy, the following orbs apply to the different bodies: Sun 17°, Moon 12°, Mercury 7,, Venus 8°, Mars 7°, Jupiter 12°, Saturn 9°, Uranus 5°, Neptune 5°. When two planets are approaching conjunction or opposition, add their respective orbs and divide by two to ascertain the arc of separation within which the aspect is supposed to be effective. For the trine and square aspects reduce the arc by one-fourth, and for the minor aspects by one-half. In all cases the closer the aspect the more powerful it becomes; also the heavier and slower moving planets are more powerful than the smaller and faster. v. Celestial sphere.

 

Orphic Mysteries. Secret rites of Dionysiac worship, supposedly founded by Orpheus. Therefore, mystic, esoteric, oracular.

 

Ortive Difference. A term sometimes applied to the difference between the primary and secondary distances, when directing the Sun at its rising or setting. It appears to indicate an effort to accommodate the fact of horizontal parallax. The term is seldom employed by modern authorities.