I didn't believe in the zodiac signs. In fact, I called everything assumptions until I sat down to read some of the "assumptions." First, I read the article on Capricorn: that is my own sign. Shockingly, everything said about me was true. Then I looked at my wife's. Again, the facts were equally true! How is this possible? Does the Bible support this? How do mere men read the destiny of others? Is astrology is a sinful study? Are they the same as the biblical magi who gave Christ gold, frankincense and myrrh?
"Stand fast now in your spells And in your many sorceries With which you have labored from your youth; Perhaps you will be able to profit, Perhaps you may cause trembling. You are wearied with your many counsels; Let now the astrologers, Those who prophesy by the stars, Those who predict by the new moons, Stand up and save you from what will come upon you. Behold, they have become like stubble, Fire burns them; They cannot deliver themselves from the power of the flame; There will be no coal to warm by Nor a fire to sit before! So have those become to you with whom you have labored, Who have trafficked with you from your youth; Each has wandered in his own way; There is none to save you" (Isaiah 47:12-14).
"If there is found in your midst, in any of your towns, which the LORD your God is giving you, a man or a woman who does what is evil in the sight of the LORD your God, by transgressing His covenant, and has gone and served other gods and worshiped them, or the sun or the moon or any of the heavenly host, which I have not commanded, and if it is told you and you have heard of it, then you shall inquire thoroughly. Behold, if it is true and the thing certain that this detestable thing has been done in Israel, then you shall bring out that man or that woman who has done this evil deed to your gates, that is, the man or the woman, and you shall stone them to death" (Deuteronomy 17:2-5).
Webster defines astrology as: "A pseudoscience claiming to foretell the future by studying the influence of the relative positions of the moon, sun, and stars on human affairs." Zodiac signs are one way to claim that the position of stars predict or dictates the events in a person's life. If such were really true, then why don't believers in such thing become fabulously wealthy and avoid all the pitfalls of life?
In reality, the descriptions you read are vaguely worded such that they can match anyone's life. People tend to accept vague statements coming from someone they think has special knowledge as applying to them. The effect is called the Barnum or Forer effect. People have a tendency to take vague statements and interpret them with their own application, making the statements seem more personal. These vague statements are used to con people into believing that the con-man has a "gift."
In other words, I could take a statement for any of the twelve zodiac signs at random and if I tell you that it is your horoscope for your sign, you will have a tendency to apply the statements in some way to your life. Thus, horoscopes and zodiac signs are fake and a form of lying. It places confidence in the works of men instead of in God, and so it is also a form of idolatry.
The magi were not interpreting signs in the stars. They had a prophecy that told them when a certain event was seen in the heavens, then it would indicate that the King of Israel, the Messiah, was born. See: Does the fact that the wise men followed a star mean that astrology is real?