Glossary
Every specialized term this platform puts on screen is defined here, from the astrological vocabulary of a chart to the astronomical quantities in its calculation details. Every definition is traceable to the verified source records it cites.
Ascendant
The point of the zodiac rising on the eastern horizon at the moment and place of a chart. It anchors the houses and changes sign roughly every two hours, which is why an accurate birth time matters. Often called the rising sign.
Aspect
An angular relationship between two points in a chart (classically the conjunction, sextile, square, trine, and opposition), which traditions read as a meaningful geometric connection between the bodies involved.
Astrology
A family of historical and contemporary practices that interpret the positions of celestial bodies as symbolically meaningful for human life. Traditions differ widely; astrology is distinct from the science of astronomy.
Astronomy
The natural science that studies celestial objects and phenomena through observation, measurement, and physical theory. Astronomy is measurable and testable; it is distinct from astrology, which is interpretive.
Birth chart
A diagram of the sky as seen from a specific place at a specific moment (usually a birth), showing the zodiac positions of the Sun, Moon, and planets, and, in most systems, the houses. Also called a natal chart.
Chart angles
The points where the great circles of the horizon and meridian meet the ecliptic: principally the Ascendant and Midheaven. They depend on the exact time and place of birth, unlike the planetary positions.
Conjunction
Two planets occupying (approximately) the same zodiac position: an angular separation near 0 degrees. Traditionally read as a fusion of the planets' significations; strictly, classical doctrine treated it as co-presence rather than an aspect.
Delta-T
The difference between the uniform time scale used for planetary calculations and time measured by the Earth's actual rotation. The Earth is not a perfect clock, so the gap has to be measured, not predicted.
Ecliptic
The plane of Earth's orbit around the Sun, projected onto the sky as a great circle. The Sun, Moon and planets all appear to travel close to it, which is why it is the reference circle astrology measures positions along.
Ecliptic longitude
How far a body has travelled around the ecliptic, measured in degrees from the vernal equinox. It is the single number every other chart label (sign, degree in sign, house) is derived from.
Element (in astrology)
One of the four classical qualities (fire, earth, air, water) used by Western astrological tradition to classify the twelve signs into groups of three. A symbolic classification inherited from Greek natural philosophy, not a scientific property.
Ephemeris
A computed table or model giving the positions of the Sun, Moon and planets over time. It is where a chart's numbers actually come from, and naming which one was used is what makes a chart reproducible.
Epoch
The reference moment a coordinate system is defined for. Because precession keeps moving the reference directions, a celestial coordinate is only unambiguous once you say which epoch it belongs to.
Equation of the equinoxes
The small difference between apparent and mean sidereal time, caused by nutation. It is reported in arcseconds and is the reason a chart states which of the two sidereal-time values it used.
Geocentric
Measured from the centre of the Earth. A geocentric position describes where a body appears from here: a choice of viewpoint, not a claim that the Earth is the centre of the solar system.
House
One of twelve divisions of a birth chart, anchored to the local horizon at the moment of the chart, which traditions associate with areas of life. Several competing house-division systems exist, such as Whole Sign and Placidus.
House cusp
The boundary where one house begins. Where a cusp falls depends entirely on the house system in use, which is why two charts for the same birth can place a planet in different houses.
Julian date
A continuous count of days used in astronomy instead of calendar dates. It has no months, leap years or time zones, which makes it the natural way to label an instant when doing arithmetic across long spans.
Midheaven
The point where the ecliptic crosses the local meridian: the zodiac degree culminating overhead at the chart's moment and place. Abbreviated MC (Medium Coeli); traditions associate it with public role and vocation.
Modality
One of three classifications (cardinal, fixed, mutable) sorting the twelve signs into groups of four by their position in the seasonal cycle. Older texts call the groups moveable, fixed, and common signs.
Nutation
A small periodic nodding of the Earth's rotation axis, superimposed on the much slower precession. It is measured in arcseconds and is one of the corrections that separates an apparent position from a mean one.
Obliquity of the ecliptic
The tilt between the ecliptic and the celestial equator: about 23.4 degrees. It is the same tilt that gives Earth its seasons, and it enters the calculation of the Ascendant and Midheaven.
Opposition
An aspect of approximately 180 degrees: two planets facing each other across the zodiac circle. Traditionally read as polarity or confrontation between the planets' significations, seeking balance between two pulls.
Orb
How far from exact an aspect may be and still count. Orbs are a convention chosen by each school rather than a measured quantity, so any figure must be stated rather than assumed.
Planet (in astrology)
In traditional astrology, one of the seven visible 'wandering stars': Sun, Moon, Mercury, Venus, Mars, Jupiter, Saturn. Modern Western practice usually adds Uranus, Neptune, and Pluto. The astrological usage differs from the modern astronomical definition.
Planetary rulership
The doctrinal assignment of each zodiac sign to a planetary ruler said to be 'at home' (in its domicile) there. Traditional and modern schemes disagree for three signs and are never silently combined on this platform.
Precession of the equinoxes
The slow circling of Earth's rotation axis, which drags the equinox point gradually around the ecliptic over roughly 26,000 years. It is why the tropical signs and the visible constellations no longer line up.
Retrograde
A planet is retrograde when it appears from Earth to move backwards along the ecliptic. It is an appearance produced by the two orbits, not a reversal of the planet itself. Direct and stationary are the other two motion states.
Sextile
An aspect of approximately 60 degrees (a sixth of the zodiac circle) between two planets. Traditionally read as an easy, cooperative connection, milder than the trine.
Sidereal time
Time measured by the rotation of the Earth against the stars rather than against the Sun. It tells you which part of the sky is overhead at a given place and instant, which is what makes an Ascendant computable.
Sidereal zodiac
The zodiac convention that anchors the twelve signs to the fixed stars rather than to the seasons. It is standard in Indian Jyotisha; the offset from the tropical zodiac is called the ayanamsha.
Square
An aspect of approximately 90 degrees (a quarter of the zodiac circle) between two planets. Traditionally read as friction or productive tension between the planets' significations.
Transit
The current, ongoing movement of a planet through the zodiac, considered in relation to the fixed positions of a birth chart. Traditions use transits as a timing technique for themes and periods, not as certainties.
Trine
An aspect of approximately 120 degrees (a third of the zodiac circle) between two planets. Traditionally read as harmony and easy flow, and classically linked to signs sharing the same element.
Tropical zodiac
The zodiac convention that fixes 0° Aries to the March equinox point, anchoring the signs to the seasons rather than to the stars. It is the standard convention of Western astrology.
Whole Sign houses
A house system in which each house is exactly one zodiac sign. The sign holding the Ascendant becomes the whole first house, and the eleven signs that follow become houses two to twelve.
Zodiac
The band of sky along the Sun's apparent yearly path (the ecliptic), divided in astrology into twelve equal 30-degree signs. The twelve-sign division originated in Babylonia and differs from the astronomical constellations.
Zodiac sign
One of the twelve equal thirty-degree divisions of the ecliptic. A sign is a measured segment of a circle, and is not the same thing as the constellation of the same name.