The symbol of Nisan is the ram, Aries. This animal is the constellation of the month, as well as the focus of the holiday of Passover, and spiritually influences the entire month. The Biblical offering brought at this time, "coincidentally", is called the "Paschal Lamb".This lamb is not merely a holiday offering; it is the symbol of Egypt and the idolatry of the Egyptians. There are more Biblical commandments surrounding this one offering than any other offering ever brought during the Temple period. This fact highlights the lamb's importance.
Historians list many gods of Egypt, yet there was a significant god that was in the form of a ram. The Bible indicates that this was the most significant god during the Hebrew enslavement. The month that the Egyptians would consider the most powerful for their god is Nisan - the full moon its most powerful day. It was precisely on this day God instructed Israel to leave Egypt, to show the impotence of idolatry. "Sorry, folks, your meaningless Ram god is powerless against the omnipotent Creator." The Torah even says to slaughter, roast, and eat the object of their idolatry. Imagine what the Egyptians must have thought when they were defeated on that day. Every year Passover shows the conviction that there's only one God. He alone is in control of every molecule of existence. Not only the lamb, but also the entire Passover Seder is a description of God's omnipotence.
This is not the only appearance of sheep in the holy writings. Sheep are a prominent feature in the Torah. The forefathers were shepherds. Rachel, who's name is another word for sheep, was a shepherdess. A famous passage relates how Jacob met Rachel while she was shepherding at a well. (See Genesis Chapter 29) Sheep were used for clothing, food, trade, and temple offerings. Abel was a Shepard. All of these references are positive, and indicate this is a more favorable sign of the zodiac.
The sheep is also a symbol of the nation of Israel. (See Psalms 44:14, Isaiah 53:7) God is referred to as The Shepard, as in Psalm 23. Israel can be as docile as a sheep being led, or as powerful as a charging ram. Yet they are vulnerable to the "wolves" of the world, and depend on their Shepard for protection. God is leader, protector, and savior.
Now is the time to remember that no matter what is going on in the world, there is a Shepherd guiding things.