Zodiac Signs were very important to the ancient worlds, they did not have TVs sets to watch, or radio for entertainment, so they watched the heavens, or outer space, for bodies which we call today planets, asteroid and comets in the heavens.
In Lunar days there are only 28 days in a month; and 13 months.
The Moon days starting with the full Moon which goes through four quarts in a month; So there is 13 Full Moons in a lunar year and three quartiles that follower each full Moon.