Defined by the math
Glossary
The core terms of astrology and the astronomy underneath them — each defined precisely, with the mathematics that makes it computable.
- Ephemeris
- A table or model of the computed positions of the Sun, Moon, and planets over time. Swiss Ephemeris — derived from NASA JPL’s DE431 integration — gives positions to about one arc-second, and is the source of every number AstralMath produces.
- Ayanamsa
- The measured angular offset between the tropical and sidereal zodiacs, currently about 24°. It grows by roughly one degree every 72 years due to precession. AstralMath uses the Lahiri definition for sidereal (Vedic) work.
- Sidereal
- A zodiac fixed to the background stars, so 0° Aries tracks a stellar reference rather than the seasons. It requires subtracting the ayanamsa from tropical longitudes and is the basis of Vedic (Jyotish) astrology.
- Tropical
- A zodiac fixed to the seasons: 0° Aries is pinned to the northern vernal equinox. Because the equinox precesses, it drifts against the stars over time. It is the basis of Western astrology.
- Nakshatra
- One of 27 lunar mansions dividing the ecliptic into 13°20′ segments in the Vedic system. The Moon’s nakshatra at birth (and its pada, or quarter) seeds the entire Vimshottari dasha timeline.
- Dasha
- A planetary period system for timing. Vimshottari, the most common, runs a 120-year cycle whose sub-periods are proportioned to the Moon’s exact position within its birth nakshatra — so the arithmetic is fixed by the ephemeris.
- Synastry
- Compatibility analysis that overlays two charts and measures the aspects one person’s planets make to the other’s. Each connection is a precise angular separation within an orb, not an impression.
- Guna Milan
- The Vedic Ashtakoota system that scores a match on eight kutas for a maximum of 36 points (gunas), computed chiefly from the two Moons’ nakshatra positions. AstralMath shows the score kuta by kuta rather than as a single percentage.
- Muhurta (electional)
- The astrology of choosing a moment: scanning a date range for times that best satisfy classical criteria for an action. Electional/muhurta work evaluates real ephemeris positions at each candidate instant and ranks them.
- Ascendant
- The degree of the ecliptic rising on the eastern horizon at the birth moment and place — the “rising sign.” It is computed from local sidereal time and geographic latitude and anchors the house framework.
- House system
- A method of dividing the chart into twelve houses of life. Time-based systems like Placidus need an exact birth time and latitude; whole-sign equates each house to a full sign. Different systems yield different cusps from the same positions.
- Retrograde
- The apparent backward motion of a planet against the stars, caused by the relative geometry of its orbit and Earth’s — not a real reversal. The ephemeris reports it exactly as a change in the sign of ecliptic longitude velocity.
- Aspect & orb
- An aspect is a significant angular separation between two points — conjunction (0°), sextile (60°), square (90°), trine (120°), opposition (180°). The orb is the allowed tolerance around the exact angle for the aspect to count.
- BaZi
- The Chinese “Four Pillars of Destiny.” Each pillar (year, month, day, hour) is a heavenly-stem/earthly-branch pair, with month boundaries set by the true solar terms — the instants the Sun reaches specific ecliptic longitudes.
See these terms on your own chart
Ascendant, nakshatra, dasha, aspects — computed from the real ephemeris, with the numbers shown.