Zodiac sign and constellation

A zodiac sign is a 30 degree slice of the ecliptic, counted from the March equinox. There are twelve slices, and they stay fixed to the seasons. When the Sun enters the first slice, it is still early spring in the northern calendar, whatever stars sit behind it that year.

A constellation is a star pattern with borders drawn around the stars. Those borders are unequal. Some patterns are wide, some are narrow, and one of them on the Sun's path is Ophiuchus, which has stars and no astrological sign.

Why the names drifted

The slice named Aries and the stars named Aries were lined up a long time ago. The Earth's axis slowly changes direction. That motion, called precession, has carried the stars away from the slices that still use their names. The Sun can sit in the Aries slice while the stars behind it belong to a different constellation.

Textbook astrology keeps the twelve equal slices. The calculator still reports them, then it reports the constellation as a second line so the two maps are not mixed. Neither line is a forecast of a person. They are two ways of naming a position on a date.

Where to check it

The zodiac sign calculator reports the sign and the constellation behind the Sun as two separate lines. The how we calculate page states the library and the limit used for those positions.