Nothing, except your gullibility if you believe in astrology. I have taught introductory astronomy at the college level for decades, and I know that there is a pervasive misunderstanding that connects astrology with astronomy. But let’s get this straight. Astronomy is a legitimate science dealing basically with the physical components of the Universe including planets, stars and galaxies. Astrology is an ancient fortunetelling practice based on the human desire to know the future. Astrology is, at best, a pseudoscience. To put it bluntly, comparing astronomy to astrology is like comparing a board certified surgeon to the activities of a medieval barber.
Humans have an amazing ability to see patterns and connections, and it is in part this ability that draws people to astrology just as surely as it draws others to astronomy and other forms of true science. The critical difference is in knowing which patterns and connections are real and meaningful, and which are simply wishful thinking, or as some prefer, “magical thinking.”
When you look with a wishful eye, you can see patterns and recognizable shapes in just about anything, from stars or clouds in the sky to tea leaves in the bottom of a cup to faces on a piece of toast to the arrangement of amorphous blobs on a shower curtain. Seeing basically random patterns and then associating them with real objects or ideas is called “pareidolia.”
When we assign meaning to such misperceived random patterns, it is called “apophenia.” The bottom line is that the human mind can see patterns where none really exist, and then assign meanings to those occurrences. There are often unrelated events that happen at the same time, so if that fits into a preconceived way of thinking it is assumed as evidence. For example, let’s say that two of your favorite singers happen to be born on the same day. Therefore they have the same Zodiacal “sign.” For someone who believes in astrology, that might “prove” that astrology is true, even though the vast majority of other singers have birthdays throughout the year, under other “signs.”
From any reasonable standpoint, that’s just a coincidence. We remember coincidences more than non-coincidences, and as such, we attribute more meaning to coincidences even though they are statistically meaningless. We don’t remember non-coincidences.
What do the following pairs have in common?
Elvis Presley & Kim Jong Un
Chuck Norris & Osama bin Laden
Jay Leno & Saddam Hussein
Well at first glance, neither member of the pair has much to do with the other. All are different nationalities; all strongly different personalities; all very different political leanings. They are all famous for one thing or another. They are all male, which is not a significant factor here. The only other factor I know of is that they each pair shares the same birthday. That’s January 8, March 10 and April 28, in order. So, from an astrologer’s standpoint, they all have the same “sign.”
Since they all share the same birthdays, one would think that astrologically they would be very similar people. But they are not. Each member of the pair is greatly different from the other member. But what is interesting is that astrologers, or just people interested in astrology, will fall all over themselves trying to find points of connection between each member of the pair. They will cherry pick often minor details to validate their beliefs. This is much the way politics works, too.
Just because we see patterns does not make them real. The untrained or mis-trained mind believes what it wants to believe, but science requires evidence. There is no valid evidence for astrology, only arbitrarily held beliefs and expectations.