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In Western astrology, astrological signs are the twelve 30 degree sectors that make up Earth's 360 degree orbit around the Sun. The signs enumerate from the first day of spring known as the First Point of Aries which is the vernal equinox. The Western astrological signs are Aries, Taurus, Gemini, Cancer, Leo, Virgo, Libra, Scorpio, Sagittarius, Capricorn, Aquarius and Pisces. The Western zodiac originated in Babylonian astrology, and was later influenced by Hellenistic culture. Each sign was named after a constellation the sun annually moved through while crossing the sky. This observation is emphasized in the simplified and popular sun sign astrology. Over the centuries, Western astrology's zodiacal divisions have shifted out of alignment with the constellations they were named after by axial precession while Hindu astrology measurements correct for shifting. Astrology has developed in Chinese and Tibetan cultures as well.

In Emoji we can find 13th sign of the Zodiac.
What is that last one? ⛎

It's Ophiuchus. Ophiuchus is one of thirteen constellations that cross the ecliptic. It has therefore been called the "13th sign of the zodiac". However, this confuses sign with constellation. The signs of the zodiac are a twelve-fold division of the ecliptic, so that each sign spans 30° of celestial longitude, approximately the distance the Sun travels in a month, and (in the Western tradition) are aligned with the seasons so that the March equinox always falls on the boundary between Pisces and Aries.

Constellations, on the other hand, are unequal in size and are based on the positions of the stars. The constellations of the zodiac have only a loose association with the signs of the zodiac, and do not in general coincide with them. In Western astrology the constellation of Aquarius, for example, largely corresponds to the sign of Pisces. Similarly, the constellation of Ophiuchus occupies most (29 November – 18 December[36]) of the sign of Sagittarius (23 November – 21 December). The differences are due to the fact that the time of year that the sun passes through a particular zodiac constellation's position has slowly changed (because of the precession of the equinoxes) over the centuries from when the Babylonians originally developed the Zodiac.

Learn more at Wikipedia.