Learn astrology · Fundamentals
Astrology glossary
Over 50 astrology terms defined plainly: ascendant, ecliptic, orb, precession, stellium, and more, with links to the detailed chapters.
8 min read · Updated 2026-06-11
An alphabetical list of the essential terms in astrology. Definitions are short (1 to 2 sentences), with a pointer to the chapter where the concept gets developed in full whenever that helps.
A
Applying aspect. An aspect whose exact angle has not yet been reached: the faster planet is closing in on the slower one. An aspect building in intensity.
Ascendant (Asc). The degree and zodiac sign rising in the east at the precise moment and place of birth. Stands for the front, surface behaviour, appearance. → chapter 8
Aspect. A notable geometric angle between two planets, measured along the ecliptic. The major aspects are conjunction (0°), opposition (180°), trine (120°), square (90°), sextile (60°). → chapter 9
Ayanamsa. The angular offset between the tropical zodiac and the sidereal zodiac. About 24.2° in 2026. → chapter 4
B
Big Three. A contemporary phrase for the Sun + Moon + Ascendant trio. Treated as the bare minimum needed to describe a person's chart. → chapter 8
C
Celestial equator. The projection of Earth's equator onto the celestial sphere. It crosses the ecliptic at an angle of 23.4°.
Conjunction. A 0° aspect (planets in the same place). Its tone is fusion, intensification, energies adding up. → chapter 9
Constellation. A grouping of stars forming a pattern recognised by a culture. The 88 modern constellations were standardised by the International Astronomical Union (IAU) in 1922. Not to be confused with a zodiacal sign. → chapter 3
Cusp. The boundary (start) of an astrological house. The cusp of H1 is the Ascendant, the cusp of H10 is the Midheaven.
D
Decan. A subdivision of a zodiac sign into three 10° portions. Each decan is tied to a particular sub-theme or to a ruling planet.
Descendant (Desc). The point opposite the Ascendant: where the ecliptic crosses the horizon in the west. The cusp of house 7. Stands for the partner, the other. → chapter 8
Domicile. The sign where a planet is "at home" (for instance, Mars in Aries, Venus in Taurus, Sun in Leo). A planet is considered especially strong in its domicile.
E
Ecliptic. The great circle on the celestial sphere that traces the Sun's apparent path over a year. The projected trace of Earth's orbit. → chapter 3
Ecliptic latitude. A body's position above or below the plane of the ecliptic, measured in degrees.
Ecliptic longitude. A body's position along the ecliptic, measured in degrees from 0° Aries (the vernal point).
Element. One of the four categories that group the signs: fire (Aries, Leo, Sagittarius), earth (Taurus, Virgo, Capricorn), air (Gemini, Libra, Aquarius), water (Cancer, Scorpio, Pisces).
Ephemeris. A table (historically) or a database (today) giving planetary positions at various moments. Astrolabica uses the astronomy-engine library.
Equal House. A house system where all 12 houses span 30° each, starting from the exact degree of the Ascendant. → chapter 7
Equinox. The moment in the year when the Sun crosses the celestial equator: the spring equinox (around 21 March, the anchor of the tropical zodiac) and the autumn equinox (around 22 September). → chapter 3
Exaltation. A sign where a planet is especially powerful (beyond its domicile). For example, Sun in Aries, Moon in Taurus, Saturn in Libra.
G
Glyph. The graphic symbol used to represent a planet (☉ Sun, ☽ Moon), a sign (♈ Aries) or an aspect (☌ conjunction).
Grand Cross. A configuration of 4 planets forming 4 squares and 2 oppositions. A major structuring tension.
Grand Trine. A configuration of 3 planets forming 3 trines (an equilateral triangle). Often within the same element. A talent configuration.
H
Hemisphere. Half of the natal chart. Hemispheres split the chart by the horizon (below = private, above = public) or by the meridian (east = the individual, west = relationship).
Horary astrology. The branch of astrology that answers a specific question by casting a chart for the moment the question is asked. More predictive than natal astrology.
Horoscope. Strictly, a person's full natal chart. In the broad, popular sense, a daily or weekly prediction for a sign.
House. One of the 12 divisions of the local sphere in a natal chart. Stands for an area of life (career, partnership, family, and so on). Depends on the time and place of birth. → chapter 6
House system. A mathematical method for slicing the local sphere into 12 houses. The main ones: Whole Sign, Equal House, Porphyry, Placidus, Koch. → chapter 7
I
IC. See Imum Coeli.
Imum Coeli (IC). The point opposite the MC: where the ecliptic crosses the meridian below the horizon. The cusp of house 4. Stands for roots, family, home. → chapter 8
J
Jyotish. Indian Vedic astrology. Uses the sidereal zodiac. A continuous practice thousands of years old.
K
Koch. A house system devised in 1962, based on trisecting the time the Ascendant takes to reach each cusp. → chapter 7
L
Lunar node. A point where the Moon's orbit intersects the ecliptic. The North Node (or Dragon's Head) symbolises future growth; the South Node (or Dragon's Tail), karmic baggage.
M
Meridian. The celestial circle running through the zenith and the north celestial pole. It sets the boundary between the east and west hemispheres of the chart.
Midheaven (MC). The culminating point of the ecliptic above the place of birth. The cusp of house 10. Stands for public vocation. → chapter 8
Mode. One of the three categories grouping the signs by dynamic: cardinal (initiator), fixed (stabiliser), mutable (adapter).
Moon (☽). In astrology, one of the two luminaries, along with the Sun. Stands for the emotions, inner rhythms, emotional security. Cycle: 28 days. → chapter 5
N
Natal chart (or sky map, natal horoscope). The graphic representation of planetary positions at the moment and place of a person's birth. The basis for any individual astrological reading. → chapter 10
O
Ophiuchus (the Serpent Bearer). The 13th constellation crossed by the ecliptic, traditionally left out of the astrological zodiac. → chapter 4
Opposition. A 180° aspect between two planets. Its tone is polarity tension, mirroring, being put in relation. → chapter 9
Orb. The margin of tolerance around the exact angle of an aspect. The smaller the orb, the more the aspect is felt. Standard: 8° for conjunction and opposition, 6° for trine and square, 4° for sextile. → chapter 9
P
Part of Fortune. A calculated point (Asc + Moon − Sun) thought to represent luck and material prosperity. Inherited from the Arabic tradition.
Personal planet. Sun, Moon, Mercury, Venus, Mars (sometimes Jupiter and Saturn). Planets that move fast enough to characterise an individual, as opposed to the slow planets (Uranus, Neptune, Pluto) that mark a generation.
Placidus. A house system devised in the 17th century, based on trisecting diurnal ecliptic time. The standard in modern Western astrology and Astrolabica's default. → chapter 7
Planet. In astrology, any celestial body used in a natal chart, by historical convention. This includes the Sun and the Moon (which are not planets in the astronomical sense). → chapter 5
Porphyry. A house system handed down from the 3rd century, based on trisecting the ecliptic arcs between the angles. Used by Co-Star. → chapter 7
Precession of the equinoxes. The slow drift of Earth's rotational axis, which moves the vernal point by about 50 arcseconds a year, about 1° every 72 years, a full cycle of about 26,000 years. The source of the tropical/sidereal offset. → chapter 4
Q
Quincunx. A minor aspect of 150°. Its tone is subtle friction, a needed adjustment.
R
Retrograde. The apparent backward motion of a planet seen from Earth, caused by the gap in orbital speeds. In astrology, a period of review and introspection. → chapter 5
S
Saturn (♄). The planet of structure, limits, the long view, maturity. Cycle: 29 years. The Saturn return around age 29 to 30 is a classic life passage.
Separating aspect. An aspect whose exact angle has been passed: the faster planet is moving away. An aspect losing intensity.
Sextile. A 60° aspect between two planets. Its tone is opportunity, cooperation, easy dialogue. → chapter 9
Sidereal. A zodiac that follows the real positions of the stars, set by a reference ayanamsa. Used in Vedic astrology. → chapter 4
Sign. One of the 12 divisions of the zodiac (Aries, Taurus...), each 30° wide. Not to be confused with the constellation (the actual astronomical object, whose divisions are uneven). → chapter 3
Solstice. The moment in the year when the Sun reaches its extreme ecliptic latitude: the summer solstice (around 21 June) and the winter solstice (around 21 December).
Square. A 90° aspect between two planets. Its tone is tension, friction, challenge, but also an engine of growth. → chapter 9
Stellium. A configuration of 3 or more planets in the same sign or the same house. Marks an overinvested zone of the chart. → chapter 10
Sun (☉). In astrology, one of the two luminaries, along with the Moon. Stands for conscious identity, vital drive. Cycle: 1 year to cross the zodiac. → chapter 5
T
T-square. A configuration of 3 planets: two in opposition plus a third squaring both. A tension you try to resolve through the "apex" planet.
Transit. A planet's current position compared to its position in a natal chart. Used to interpret the periods a person is going through.
Trine. A 120° aspect between two planets. Its tone is harmony, flow, innate talent. Often within the same element. → chapter 9
Tropic. The extreme circle of terrestrial latitude reached by the Sun at the solstices: the Tropic of Cancer (23.4° N) and the Tropic of Capricorn (23.4° S). The source of the name "tropical zodiac".
Tropical. A zodiac anchored on the seasons (0° Aries = the spring equinox). The standard in modern Western astrology. → chapter 4
U
Uranus (♅). The planet of rupture, originality, freedom. Discovered in 1781. Cycle: 84 years.
V
Vedic astrology. See Jyotish.
Vernal point. The point on the ecliptic where the Sun crosses the celestial equator at the spring equinox. The origin of the tropical zodiac (0° Aries).
Vertex. A calculated point on the west side of the chart, sometimes tied to "fated" encounters. Modern astrology.
W
Whole Sign. A Hellenistic house system where each house matches a whole sign, starting from the Ascendant's sign. The oldest and the simplest. → chapter 7
Z
Zodiac. A band about 16° wide centred on the ecliptic, divided into 12 signs of 30° each. The reference frame for placing the Sun, Moon and planets in astrology. → chapter 3