Astrology Glossary: Birth Chart Terms, Clearly Explained

The chart and the signs

Birth chart (natal chart)

A map of the sky for the exact moment and place you were born: where the Sun, Moon and planets were in the zodiac, which degree was rising on the eastern horizon, and how the twelve houses fell. Everything else in this glossary is a part of it. Your birth chart draws it and reads it for you.

Zodiac signs

The twelve 30° sections of the ecliptic, the Sun's apparent yearly path, from Aries to Pisces. A sign describes how a planet in it behaves. You have many signs in your chart, one for each planet and point, not only your Sun sign. The 12 signs covers each one.

Tropical zodiac

The zodiac used in Western astrology, and by Celestio. It starts 0° Aries at the March equinox, so the signs follow the seasons rather than the constellations.

Sidereal zodiac

The zodiac used in Vedic astrology, fixed to the stars. Because the equinoxes slowly drift against the stars, the two zodiacs are now about 24° apart, so a planet in the first 24° or so of a tropical sign usually falls in the previous sign in the sidereal zodiac. Neither is wrong; they measure different things, the seasons and the stars.

Sun sign

The sign the Sun was in when you were born: your "star sign". It describes your core identity, will and vitality.

Moon sign

The sign the Moon was in when you were born. It describes your emotional needs and instinctive reactions. The Moon changes sign about every two and a quarter days, so on a little under half of all days it changes sign at some point, and a birth time decides which one is yours. More in find your Moon sign.

Rising sign (Ascendant)

The sign of the exact degree of the zodiac that was rising on the eastern horizon at your birth. It is not the sign the Sun was in at sunrise. It describes how you meet the world and starts the 1st house. The rising sign changes about every two hours on average, but at mid-northern latitudes some signs rise in about an hour and others take close to three, so your birth time matters. See what's my rising sign.

Big Three

Your Sun, Moon and rising signs together, the quickest summary of a chart. The name is modern shorthand, but the trio itself is old: Hellenistic astrologers built their charts around the Sun, the Moon and the Ascendant. See your Big Three.

Elements

Four groups of three signs that share a temperament:

• Fire (Aries, Leo, Sagittarius): active, warm, enthusiastic.
• Earth (Taurus, Virgo, Capricorn): practical, steady, physical.
• Air (Gemini, Libra, Aquarius): mental, social, curious.
• Water (Cancer, Scorpio, Pisces): emotional, intuitive, protective.

Modalities

Three groups of four signs that share a way of moving: cardinal signs start things (Aries, Cancer, Libra, Capricorn), fixed signs hold and sustain them (Taurus, Leo, Scorpio, Aquarius), and mutable signs adapt and change them (Gemini, Virgo, Sagittarius, Pisces).

Cusp

The starting boundary of a house, or of a sign. "Born on the cusp" is popular shorthand for a birthday near a sign change, but the Sun is always in one sign at any moment. The exact time it changes sign varies from year to year, so someone born on the 21st of a month can belong to either sign, and a chart for the exact moment settles it.

Decan

A 10° third of a sign. There are two schemes. The traditional one gives each decan to a planet in a fixed order (these are also called faces). The modern one gives each decan to a sign of the same element, so the second decan of Aries is said to have a Leo flavour.

Angles and houses

Angles

The four points where the horizon and the meridian cross the ecliptic: the Ascendant (east), the Descendant (west), the Midheaven (top) and the IC (bottom). Planets close to an angle are among the most visible in a chart.

Descendant

The degree setting on the western horizon, directly opposite the Ascendant. It starts the 7th house and describes what you look for in partners. See the 7th house.

Midheaven (MC)

The degree of the zodiac at its highest point on the meridian at your birth. It is not the point directly overhead. It describes your public direction, vocation and reputation. In Placidus and other quadrant systems it is the 10th house cusp; in Whole Sign houses it can fall in the 9th, 10th or 11th house. See the Midheaven.

IC (Imum Coeli)

The degree directly opposite the Midheaven, at the bottom of the chart. It describes home, roots, family and your private foundations, and in quadrant systems it starts the 4th house.

Houses

The twelve sections of the chart wheel, each an area of life: self, resources, communication, home, creativity, work and health, partnership, shared resources, belief and travel, vocation, friends and groups, and the hidden life. Signs say how, planets say what, houses say where. See the 12 houses.

House cusp

The degree where a house begins. Its sign colours that area of life even when no planet sits there: Libra on the 7th house cusp brings Libra's tone to your partnerships.

House system

The method used to draw the house cusps. Systems differ in how they divide the sky, so a planet near a cusp can change house from one system to another. The meaning of each house stays the same.

Placidus houses

The most widely used house system in modern Western astrology, and the one Celestio uses. It divides the time each degree takes to travel between the angles into thirds, so houses come out unequal in size. It cannot be drawn beyond about 66° north or south, where Celestio uses Whole Sign houses instead. See Placidus and other house systems.

Whole Sign houses

The oldest house system: the rising sign is the whole 1st house, the next sign the whole 2nd, and so on, one sign per house. See Whole Sign vs Placidus.

Intercepted sign

A sign that sits entirely inside one house without touching any house cusp. It happens in unequal house systems such as Placidus, more often at higher latitudes, and never in Whole Sign or Equal houses.

Empty house

A house with no planets in it. It is still active: its cusp sign and that sign's ruling planet describe how that area of life works for you. See empty houses.

Planets and points

Planets

In astrology, the Sun and Moon count as planets alongside Mercury, Venus, Mars, Jupiter, Saturn, Uranus, Neptune and Pluto. Each planet is a drive or function: the Moon your feelings, Mercury your mind, Venus love and values, Mars desire and drive, Saturn structure and time. See meet the planets.

Luminaries

The Sun and the Moon, the two lights of the chart.

Personal, social and outer planets

The personal planets (Sun, Moon, Mercury, Venus, Mars) move fast and differ even between people born weeks apart. The social planets (Jupiter, about 12 years around the zodiac, and Saturn, about 29.5) mark the chapters of a life. The outer planets (Uranus, Neptune and Pluto) stay in a sign for years, so their signs describe generations; they become personal when they sit on an angle or touch a personal planet closely.

Rulership

Each sign has a ruling planet: Mars rules Aries, Venus rules Taurus and Libra, and so on. For three signs, astrologers differ: traditional astrology gives Scorpio to Mars, Aquarius to Saturn and Pisces to Jupiter, while modern astrology gives them to Pluto, Uranus and Neptune, often keeping the older ruler as a co-ruler.

Chart ruler

The planet that rules your rising sign. Its sign, house and aspects describe the direction your life tends to take. See your chart ruler.

Dignity and debility

How comfortable a planet is in its sign. A planet is strongest in its own sign (domicile) and in its sign of exaltation, and weakest in the sign opposite its own (detriment) and the sign opposite its exaltation (fall). Venus is at home in Taurus and Libra, exalted in Pisces, in detriment in Scorpio and Aries, and in fall in Virgo.

Sect

Whether a chart is a day chart (the Sun above the horizon at birth) or a night chart. Traditional astrology splits the planets into a day team (Sun, Jupiter, Saturn) and a night team (Moon, Venus, Mars), with Mercury joining whichever side it rises on. Planets on the chart's own team tend to work more smoothly; Mars in a day chart and Saturn in a night chart are read as the more demanding ones.

Lunar nodes

The two points where the Moon's orbit crosses the ecliptic: the North Node, where it crosses heading north, and the South Node, directly opposite. They move backwards through the zodiac, completing a circle in about 18.6 years, and eclipses happen near them. The mean node is a smoothed average that always moves backwards; the true node follows the Moon's actual orbit and wobbles around it, so the two can differ by a degree or more. See the lunar nodes.

Part of Fortune

A calculated point built from the Sun, the Moon and the Ascendant. By day it is Ascendant + Moon − Sun. Most traditional astrologers reverse it by night (Ascendant + Sun − Moon), though Ptolemy did not, which is why calculators sometimes disagree for night births. It is read for body, circumstance and fortune in the material sense.

Chiron

A small body discovered by Charles Kowal on 1 November 1977, orbiting the Sun between Saturn and Uranus about every 50 years. Its orbit is very uneven, so it spends years in some signs and only a short time in others. Astrologers began using it after its discovery, as the "wounded healer": a tender spot that becomes a source of wisdom.

Lilith

Several different things share this name, which is why charts disagree:

• Mean Black Moon Lilith is the average position of the Moon's apogee, the far point of its orbit. It moves steadily forward, about nine months per sign. This is what most charts mean by Lilith.
• True (osculating) Lilith is the apogee of the Moon's instantaneous orbit. It swings up to about 30° either side of the mean, so it can sit in a different sign.
• Asteroid Lilith (number 1181) is a real asteroid, a different point altogether.

Astrologers read Lilith as the raw, refused or untamed side of the self.

Stellium

Three or more planets gathered in one sign or one house, which concentrates the chart's emphasis there. Older astrologers kept the word for rarer clusters of four or five. See stellium meaning.

Aspects

Aspect

An angle between two planets or points, measured along the zodiac. Aspects show how the parts of a chart work together or rub against each other. See the guide to aspects.

Orb

How far from exact an aspect can be and still count. There is no single standard: modern astrologers usually give each aspect an orb (wider for conjunctions and oppositions), while astrologers of William Lilly's era gave each planet an orb and averaged the two. Different orb settings are the usual reason two charts list different aspects.

Major aspects

• Conjunction (0°): two planets together; their energies fuse.
• Sextile (60°): easy cooperation that rewards a little effort.
• Square (90°): friction that pushes for action and growth.
• Trine (120°): natural flow and talent.
• Opposition (180°): a pull between two sides that asks for balance, often felt through other people.

A hard aspect is not a bad one. Squares and oppositions are often where a chart's drive comes from, and traditional astrologers judge the planets involved as much as the angle.

Quincunx (inconjunct)

An angle of 150°, between signs that share neither element nor modality. It feels like an awkward adjustment between two parts of you that do not naturally speak the same language.

Applying and separating aspects

An aspect is applying when the faster planet is still moving towards the exact angle, and separating when it has passed it. Applying aspects are read as stronger, the theme still building.

Out-of-sign aspect

An aspect that is within orb by degree but falls in signs that do not usually make that aspect, such as 29° Scorpio and 2° Pisces, which are 93° apart but in two water signs. Astrologers disagree on whether to count it.

Aspect patterns

Shapes made by several aspects together. A T-square is two planets in opposition, both square a third; a grand trine is three planets about 120° apart, usually in one element; a yod is two planets in sextile, both quincunx a third.

Movement and timing

Ephemeris

A table of planetary positions by date. Modern astrology software mostly uses the Swiss Ephemeris, which is built from NASA's Jet Propulsion Laboratory data.

Ingress

A planet's entry into a new sign, such as the Sun's ingress into Aries at the March equinox.

Retrograde

The apparent backward motion of a planet against the zodiac, as Earth overtakes it or it overtakes Earth. The planet does not actually reverse. The Sun and Moon are never retrograde. Mercury goes retrograde three or four times a year for about three weeks; the slower planets for months at a time each year.

Station

The point where a planet appears to stand still as it turns retrograde or direct. A planet stationing near the day you were born is read as especially strong in your chart.

Transit

A planet's current position in the sky compared with your birth chart. When a moving planet reaches one of your natal planets or angles, it brings a temporary theme to that part of your life. See astrological transits.

Saturn return

Saturn's return to the exact degree it held when you were born, first between about ages 28 and 30, then between about 58 and 60. See Saturn return.

Progressions and solar returns

Two other timing methods. Secondary progressions treat each day after birth as one year of life. A solar return is a chart for the moment each year when the Sun comes back to its exact birth position.

Relationships

Synastry

Comparing two birth charts by laying one over the other and reading the aspects between one person's planets and the other's. See what is synastry.

House overlay

Where one person's planets fall in the other person's houses, showing which areas of your life someone tends to light up. See synastry house overlays.

Composite chart

A single chart for a relationship, made from the midpoints between two people's planets. It describes the relationship as its own entity. See composite chart vs synastry.

Compatibility report

A written reading of two birth charts together: what draws two people together, how they talk and disagree, and what holds the connection. Celestio writes them for partners, crushes, friends and family. See compatibility.