Glossary
Plain definitions of the astronomy and astrology terms used across the otldr reference pages. For the broader context, start with astrology vs astronomy.
- Ascendant (rising sign)
- The zodiac sign rising on the eastern horizon at a given moment and place. It sets where the houses of a chart begin and changes about every two hours.
- Aspect
- The angular distance between two bodies on the chart wheel. Significant angles include the conjunction (0°), sextile (60°), square (90°), trine (120°) and opposition (180°).
- Cardinal / Fixed / Mutable
- The three modalities. Cardinal signs begin a season, fixed signs sustain it, mutable signs end and transition out of it.
- Conjunction
- An aspect of about 0° — two bodies at the same point on the wheel, read as a blending of their energies.
- Decan
- A 10° subdivision of a sign; each sign has three decans, giving 36 in all, each with its own traditional subruler.
- Ecliptic
- The apparent yearly path of the Sun across the sky, and the plane against which planetary longitudes are measured.
- Element
- One of fire, earth, air or water. Each zodiac sign belongs to exactly one element; signs of the same element sit 120° apart.
- Ephemeris
- A table or computation of celestial positions over time. otldr computes its ephemeris rather than transcribing one.
- Gibbous
- A Moon phase more than half but not fully lit — waxing gibbous before full, waning gibbous after.
- House
- One of twelve divisions of the chart representing an area of life (self, money, partnership, career, and so on). Houses depend on the exact birth time.
- Ingress
- The moment a body crosses from one zodiac sign into the next. The Sun's ingress into Aries marks the spring equinox.
- Luminary
- The Sun or the Moon. Although neither is a planet astronomically, astrology counts both among the ten 'planets' of a chart.
- Modality
- See cardinal / fixed / mutable — the quality describing how a sign acts within its season.
- Natal chart (birth chart)
- A map of the sky for the exact time and place of a birth, drawn as a 360° wheel of planets, signs, houses and aspects.
- Opposition
- An aspect of about 180° — bodies on opposite sides of the wheel, read as tension or polarity.
- Precession
- The slow ~25,800-year wobble of Earth's axis. It is why the tropical signs no longer line up with the same-named constellations.
- Retrograde
- The apparent backward (westward) motion of a planet as seen from Earth, caused by the two bodies' differing orbital speeds. The planet does not actually reverse.
- Sidereal month
- The ~27.3 days the Moon takes to orbit Earth once relative to the stars — shorter than the synodic month.
- Square
- An aspect of about 90°, read as friction or a challenge that demands action.
- Station
- The moment a planet appears to pause before changing between direct and retrograde motion. A body 'stations retrograde' or 'stations direct'.
- Synodic month
- The ~29.53 days between one new moon and the next — the cycle the Moon's phases follow.
- Trigon
- A triangle of three signs that share an element, each 120° from the next.
- Trine
- An aspect of about 120°, traditionally read as ease or support between two bodies.
- Tropical zodiac
- The Western system that fixes 0° Aries to the spring equinox and divides the sky into twelve equal 30° signs, independent of the constellations.
- Waxing / Waning
- Waxing means the Moon's lit portion is growing (new toward full); waning means it is shrinking (full toward new).