With the change, the birth days assigned to particular zodiac signs might not be accurate anymore.
Minnesota Planetarium Society board member Parke Kunkle said in an interview with Minnesota Star Tribune that the ancient Babylonians based zodiac signs on the constellations the Sun was "in" on the day a person was born.
Over time, the moon's gravitational pull has made the Earth "wobble" around its axis, creating a one-month bump in the stars' alignment.
"When [astrologers] say that the Sun is in Pisces, it's really not in Pisces," Kunkle said in the interview.
Because of additional one month in the cycle, the birthday classifications under each zodiac sign changed as follows:
Science news website LiveScience explained that early astronomers calculated the old zodiac signs based on the position of the sun as it's perceived from the revolving earth. Based on this position, the sun passes through the constellations that formed the zodiac signs - Aries, Taurus, Gemini, Cancer, Leo, Virgo, Libra, Scorpio, Sagittarius, Capricorn, Aquarius and Pisces.
Originally, the zodiac signs were determined based on the constellation the sun was "in" on the day a person is born. Astronomers observed the sun's travel through the signs of the zodiac in the course of one year, spending about a month in each.
However, a movement of the Earth called "precession" causes the Earth to continually move around its axis. The gravitational attraction of the moon on the Earth causes the movement, causing the signs to slip one-tenth — equivalent to one month — of the way around the sky.
Because of the movement, the sun may no longer be within the constellation of a sign during a particular period. For example, those born between March 21 and April 19 consider themselves to be Aries, but the sun is actually in the constellation Pisces on that period.
The new sign, Ophiucus, is the constellation right after Scorpius.
According to a report on news.com.au, the ancient Babylonians were believed to have removed the 13th sign because the 12 signs align more accurately with the calendar.
Ophiucus, the new addition to the zodiac sign family, is represented by a serpent tamer, holding a serpent with his two hands. The new sign is associated with higher education, healing and medicine.