In Parshat HaChodesh (Shmot 12:3) Moshe and Aharon are told:
Speak to the whole community of Israel and say that on the tenth of this month each of them shall take a lamb to a family, a lamb to a household.
According to Ramban:
The reason for this commandment is that the constellation of Aries (the Ram) is at the height of its power during the month of Nisan, it being the sign of the zodiac that ascends the heavens.
Rabbi Dr. Charles B. Chavel explains that there are twelve signs of constellations in the zodiac, an imaginary belt encircling the heavens, revolving around the sun. Each month, another constellation begins the procession of the signs in their course around the heavens. The ram is the first sign of the zodiac in the month of Nisan.
Therefore, He commanded us to slaughter the sheep and to eat it in order to inform us that it was not by the power of the constellation that we went out of Egypt, but by decree of the Supreme One. According to the rabbis (Rambam, Moreh Nevuchim III:46) the Egyptians worshipped it as a deity, He has all the more informed us through this that He subdued their gods and their powers at the height of their ascendency. And thus the rabbis have said (Shmot 12:21): “Take your lambs and slaughter” the gods of Egypt.
Aruch HaShulchan 429 points out that Pharaoh relied on Aries for his strength and luck. In the plague of darkness, Pharaoh wasn’t worried because he knew that the month of Nisan was approaching and he was sure that Aries would bring him good luck.
That is why God said to Moshe and Aharon (Shmot 12:2):
This month shall mark for you the beginning of the months; it shall be the first of the months of the year for you.
Aruch HaShulchan explains:
This month that Pharaoh is waiting for will be the beginning of the months for you, in which it will become clear that there is no truth in the zodiac. HaShem is our God in the Heavens above and on the earth below, there is no other God. And Israel is His chosen nation. Therefore, it is the first month for you.
Should we believe in astrology as it is part of nature and God ultimately created everything?
We learn in a Midrash in Eicha Rabbah 3:8:
Rabbi Abbahu said in the name of Rabbi Yochanan: A king entered a province and had with him generals, captains and military commanders and the notables of the province were sitting in its midst. One of them said, “I will take a general to my house.” Another said, “I will take a captain to my house”; while still another said, “I will take one of the commanders to my house.” But a shrewd man there said, “I will take the king, because while the others may pass away the king will not do so.”
Similarly there are idolaters who worship the sun, others the moon, and still others wood and stone; But Israel worship God alone.
Nisan had to be the first month, in order to prove to both Pharaoh and B’nai Yisrael that God is above the zodiac.