Undiscovered stars learned
Ophiuchus, 13th constellation of zodiac
13 Not 12 Constellations in the Zodiac, NASA Points Out
https://science.howstuffworks.com/science-vs-myth/everyday-myths/13-not-12-constellations-the-zodiac-nasa-points-out.htm
https://spaceplace.nasa.gov/starfinder2/en/
The Babylonians lived over 3,000 years ago. They divided the zodiac into 12 equal parts–like cutting a pizza into 12 equal slices. They picked 12 constellations in the zodiac, one for each of the 12 "slices." So, as Earth orbits the Sun, the Sun would appear to pass through each of the 12 parts of the zodiac. Since the Babylonians already had a 12-month calendar (based on the phases of the Moon), each month got a slice of the zodiac all to itself.
OphiuchusBut even according to the Babylonians' own ancient stories, there were 13 constellations in the zodiac. (Other cultures and traditions have recognized as many as 24 constellations in the zodiac.) So the Babylonians picked one, Ophiuchus, to leave out. Even then, some of the chosen 12 didn't fit neatly into their assigned slice of the pie and slopped over into the next one.