Twelve equal sections of a circle
The ecliptic is the apparent yearly path of the Sun. Tropical astrology starts Aries at the March equinox and divides the full 360° circle into twelve sections of 30° each. Taurus begins at 30°, Gemini at 60°, and the sequence continues around the circle. A body at 5° Taurus has 35° of tropical ecliptic longitude. This is a coordinate convention; the named zodiac sign is not the same thing as a visible constellation. Constellation boundaries vary in size, while every zodiac sign has the same angular width.
Why the printed date ranges vary
A newspaper range such as “March 21 to April 19” is a useful shorthand for the Sun, but an ingress occurs at a particular instant. Calendar year, time zone, and the moment chosen by a source can shift the civil date displayed at a boundary. Someone born close to an ingress should use the actual birth date and time with a calculator that states its zodiac and time standard. The Moon changes signs much faster than the Sun; its position can remain uncertain when a birth hour is missing. The Ascendant depends still more strongly on time and place.
Sun, Moon, rising, and the rest of the chart
A sun sign tells which tropical section held the Sun at birth. The Moon, planets, and Ascendant each have positions of their own. For example, two people with the same Sun sign can have different Moon signs, different aspects, and different house layouts. In an astrological reading, the sign suggests a style through which a particular planet is interpreted; the planet identifies the topic. Treat a “Taurus” description as a discussion of the Sun in Taurus only when it is actually labeled that way. A sign is not an all-purpose personality type.
Choose a convention before comparing sites
Tropical and sidereal zodiacs use different reference points. A sidereal calculation needs a named ayanamsa or other offset convention; neither system can be silently substituted for the other. House systems are a separate setting and do not move the tropical longitude of a planet. When two sites disagree, compare the exact instant, UTC offset, selected zodiac, rounding, and whether one has guessed a missing birth time. Meanings attached to signs are historical interpretations rather than experimentally verified personality measurements.
Related guides and tools
- Calculate a tropical birth chart
- Sun and Moon placement guides
- Compare tropical and sidereal positions
- Read sign and degree in an ephemeris
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Updated 20 September 2026