Zodiacs and Earth’s Precession

You may have seen recent posts claiming that NASA published some new results on the zodiac signs. Some of the bigger internet publishers, like Distractify, have popularized the story. The story says there is a 13th sign we haven’t seen before and all the zodiacs need to have their dates adjusted.

For clarity, NASA has no opinions about astrology. They never have and the won’t any time soon.  And there is no 13th sign. Snopes, bless their hearts for their wonderful works, called this out clearly.

However, your sun sign still might not be safe… depending on your level of trust in the basic components of your zodiac’s definition. Traditionally your zodiac, or sun sign, is defined to be the constellation that the sun is in on the morning of your birth. This is reliable from year to year because we travel around the sun once. So the sun cycles through each section of the sky in a big arc.

However, the location of the sun is strongly controlled by the location of earth’s axis in relationship to the rest of the sky. The tilt of earth’s axis rotates every 22,000 years- this is called Precession. Many ancient cultures knew about this and it is well studied and validated. Precession causes the zodiacs to slide backwards through the season at a rate of one sign shift each 1.2kyr. Even the Greeks noticed that the zodiac signs were slowly cycling, or regressing, through the seasons.

The Greeks wanted to stop this from happening so Ptolemy, a famous Astronomer who worked in Alexandria, fixed the astrological signs to the equinoxes and seasonal changes.  From then on, the western notions of zodiac signs are now more tied to local seasonal elements than to the solar systems located many light years away. These are the definitions we use today! This means that there is no way for NASA (or anyone else!) to scientifically reinvent them. Timing of zodiac signs are kind of like math definitions. Humans defined them, so there is no scientific way that NASA could ever prove them wrong. There is nothing to prove, timing of each zodiac is just a definition applied by Ptolemy.

If you are someone who happens to believe deeply in astrology, then it’s deeply unlikely that anything in this article will effect that way you view your zodiac sign. However, I think it’s interesting to note that if you believe in Astrology, then you implicitly believe that the time of year you were born in affects your personality. This belief in zodiac signs could mean you would also appreciate research on seasonal affective disorder. Or you might really want to check out this fabulous article by the Atlantic which discusses recent research showing people born in the summer are more susceptible to mood swings (and many other personality quirks that are seasonally significant!).

This is one situation where science, math, and astrology aren’t always well separated. Science can tell us something about the world around us. And, historically, humans built belief systems around that knowledge (Astrology).  Then we had to update the astrological belief system when the science no longer matched. Because initially, sun sign was a good indicator, until we learned about Precession. So astrology must be adjusted to match the seasons, not the stars. Which, some argue, is what the sun signs were supposed to do anyways. And, while we can understand Precession scientifically, we can’t prove anything about the tenants of astrology. Perhaps it’s only a matter of time until we find more scientific reasons to support certain aspects of Astrology? Certainly much of the internet is ready to believe that NASA should be able to weigh in.



About Samantha from SocialMath

Applied Mathematician and writer of socialmathematics.net.
This entry was posted in Communicating Math, Media, Nature and tagged , , , , , , , . Bookmark the permalink.

3 Responses to Zodiacs and Earth’s Precession

  1. Andybachhav says:

    Got something new to learn today,….. thxxxxx a lot!!!

  2. Pingback: #Zodiacs and Earth’s Precession — Social Mathematics – Ola Queen Bee of Astrology

  3. Oh, Ptolemy, you telling the universe what to do.

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