In both astrology and historical astronomy, the Zodiac is a circle of twelve 30° divisions of celestial longitude that are centered upon the ecliptic. The ecliptic is the apparent path of the Sun across the celestial sphere over the course of the year.
Although the zodiac remains the basis of the ecliptic coordinate system in use in astronomy besides the equatorial one, the term “zodiac” and the names of the twelve signs are today mostly associated with horoscopes and astrology.
The paths of the Moon and visible planets remain close to the ecliptic, within the belt of the zodiac. They are regular divisions and do not correspond exactly to the twelve constellations after which they are named. We commonly call these twelve divisions “signs.” You can say that you were born under the sign of Libra, or take the scientific path and see the zodiac as a celestial or ecliptic coordinate system, which takes the ecliptic as the origin of latitude, and the position of the Sun at vernal equinox as the origin of longitude.
The term “zodiac” derives from Latin zōdiacus, which in its turn comes from the Greek zōdiakos kyklos, meaning “circle or pathway of animals.” Half of the signs of the classical Greek zodiac are represented as animals (plus two mythological hybrids).
You may think that you were “born under a bad sign” (which is really a blues song by Albert King) and that “If it wasn’t for bad luck, I wouldn’t have no luck at all” but what if you were born under a forgotten sign?
The 12 signs of the Zodiac that are familiar to us from astrology and horoscope advice (Aries, Taurus, Gemini, Cancer…) does not include the 13th or “forgotten” constellation: Ophiuchus.
If there is a “bad sign” I would guess it might be Ophiuchus with its number 13 and forgotten status. The sun moves in front of Ophiuchus from about November 30 to December 18 each year but I doubt that you have ever heard someone say they were born when the sun was in Ophiuchus.
Every year at this time, I notice a post from earthsky.org to look for this faint constellation, also known as the Serpent Bearer, as it appears in the southwest sky on late August and September evenings. It is above the bright ruddy star Antares, which is the brightest in the constellation Scorpius the Scorpion.