O:

Oblateness: how much a planet has been flattened at its poles by its rotational speed. If the Earth’s size and rigidity were proportionately reduced, it would be similar to a basketball of butter. Now for all spinning balls, the part furthest from the spin axis spins the fastest, like the person at the end in crack the whip. And since the parts of a planet at its equator are furthest from its pole (which is its spin axis), it follows that a planet’s equatorial part has the greatest tendency to fly away. Thus all spinning heavenly bodies are wider through their equators (their "equatorial diameter") than through their poles (their "polar diameter"). This effect increases as a planet spins faster, and decreases the denser the planet is. The Earth, with a density of 5.5 g/cm3, has an equatorial diameter 27 miles greater than its polar diameter, or an oblateness of 0.3%. Saturn, a gas giant that would float in water with a density of only 0.687 gm/cm3 (the density of water is 1 gm/cm3 ), is 8078 miles thicker through its equator than through its poles. Its oblateness is 10%. If a planet’s equatorial diameter is De and its polar diameter is Dp, then its oblateness is defined as (De - Dp)/De.

On the (house) cusp: when a house cusp falls within a sign, that sign is said to be on (or to "fall" on) the cusp of that house. That sign and its ruling planet are then said to rule the affairs of that house.

Oort cloud: A Dutch astronomer, Jan Oort, observed in 1950 that no comet had ever been seen with an orbit indicating that it came from interstellar space, nor did comets seem to have a preferred direction of origin. He therefore hypothesized that the Sun is surrounded by an immense cloud of comets - the Oort Cloud - extending from about 1200 times Pluto’s distance from the Sun out to about 3 light years. (The nearest star, Proxima Centauri, is 4.25 light years away.) So distant that its members are only weakly bound to the Sun, the Oort Cloud is occasionally disturbed by passing stars that fling bits of it either into the inner solar system as comets or out into interstellar space. The Oort Cloud is thought to contain as many as a trillion comets, but since they are so small and at such a great distance, there is no direct evidence that it actually exists at all.

Opposition: the 180° aspect (orb 10°-12°) denoting change, polarity, awareness, objectivity, and often a particular way or style of relating. This is the second strongest aspect and symbolizes a conflict between an internal energy (initially not seen as internal), and an apparently external one (that one fails to see in oneself, and, like the Seventh house, projects onto the outer world). The opposition signifies others we bring into our life to externalize unconscious or rejected aspects of our own being. Accepting these is the growth in consciousness the conflict provides.

Orb: the greatest deviation that an aspect can have from being exact and still be in effect. Orbs are highest for the Sun and Moon, smaller for the inner planets, and smallest for the outer planets (see the rightmost, upper table on page one). Orbs decrease as the aspect’s harmonic number increases (e.g., the orbs for the semisextile and conjunction of the Sun and Moon are respectively 2° and12°).

Outer Planets: Uranus, Neptune, and Pluto. Since they remain 7, 14 and 12 - 33 years respectively in a sign, their effect by sign is generational, collective, and social, rather than individual. The effects of these planets by house, however, are very individual, particularly in the Angular houses. (Pluto stays 12 to 33 years in a sign because its orbit is so highly elliptical.)