Buckle up because I'm about to go on an Astrology rant right now...
First of all, this 13th Zodiac Sign is old news. Like, Babylonian old. But also, do any of y'all read? This Astrology "news" comes out as breaking news every now and then thanks to random people on social media just discovering Ophiuchus in a Time Magazine article that was posted online in January of 2011. Then they tweet about how their lives are now over. Okay.
Astrology is something else. It's not science. -NASA
NASA then goes on to say (in 2011!), "Hey guys, Astronomy and Astrology are different--we don't know what Astrology is really but, stop freaking out because it's not science" (in so many words). Here's the thing--yes they're different (duh). While Astronomy is the scientific study of outer space, Western Astrology is the intuitive art of interpreting the patterns that exist based off of the seasons, as well as some Astronomy. Got it? Good.
“Astrology is geocentric. It relates life on Earth to the Earth’s environment, and seasons are the most dramatic effect, which is why we use the tropical zodiac.” -Jeff Jawer, CNN
The thing is, there is no 13th Zodiac Sign, so long as you follow the Tropical Zodiac, like we do in Western Astrology, and not the Sidereal Zodiac, like they do in Eastern Astrology. The Sidereal Zodiac is fixed to the actual constellations, whereas the Tropical Zodiac follows the patterns of the seasons. The Babylonians discovered many constellations, including Ophiuchus, and they picked the 12 signs of the Zodiac based on how they were spaced out between each other, as they corresponded with the months and changing seasons. They determined this from how they saw the stars from Earth (not where the stars actually were in space). So when the "Sun is in Pisces," it's not really in Pisces. Using the Sidereal Zodiac, it is.
So why do we use the Tropical Zodiac and not the Sidereal Zodiac? Good question. Because in Western society, once Astrology was no longer deemed a science in the 17th Century (The Age of Reason), we stopped continuing to study Astrology, which has subsequently made us stuck in the Babylonian way of interpretation. I'm not saying one is right over the other (although NASA seems to think so), but maybe we should be having more conversations about Astrology instead. Tropical Astrology has fairness to it, in regards to the 12-month cycle and the changing of the seasons holding value. And if we did switch to Sidereel Astrology, everyone's signs will more than likely change, regardless of the 13th sign. But just so everyone knows: an Astrologer named Walter Berg published a book on the official 13 Sign Zodiac, using the Sidereel Zodiac. This was published in 1995 (!!!), which is why all of this is very well known in the East, or to people in the West that actually study Astrology. Glad we cleared that up. Awesome.
A myth I also want to de-bunk right now: Astrology does not make claims to "know" the future--or at least not in the way that you think. Astrology is a way of predicting when we'll feel the different energies (and various combinations of them) that we feel from the planets. It's a way of understanding your personality and behavior, and can be an extremely helpful tool in understanding yourself in the interest of personal growth. That's why psychologists like Carl Jung studied Astrology--you know your Myers-Briggs sign? That's based off of Carl Jung's archetype work, which is based off of Astrology.
Now let's move on to Natal Charts. You have always been told you have a horoscope sign based on your date of birth. Yes, this is true, but you are referring to your "Sun Sign." Imagine the zodiac as a wheel (or circle), and then a wheel of "Houses" inside of it.
"The zodiac wheel is based on the sun's apparent yearly rotation about our Earth (along the ecliptic), while the wheel of Houses is based on our Earth's 24-hour rotation about its own axis. The 2 wheels join together at points derived by calculations involving your exact birth time and astronomical birth coordinates. Then, the planets are described in 2 ways: as being in a zodiac sign, and also as being in a House." -Corrine Lane
Your Houses are determined down to the second you were born. If you don't know the time you were born, you can still learn a lot based off of your planets, however, you won't get a thoroughly accurate and detailed interpretation.
Let's use my birthday as an example. I was born on December 18. A Sagittarius is born between November 22 and December 21, so that is my sun sign. Now, taking into consideration the exact time and location of my birth (you need the location so you can interpret that specific time zone), this is what my Natal Chart looks like. If you'd like to check out yours (for free), I recommend this website.
Tropical Natal Chart:
So you see, my sun is in Sagittarius, but also my moon is in Taurus and my Rising Sign or 1st House (also referred to as your Ascendant) is in Scorpio--in addition to all of my other planets and houses, which all mean something.
For example, my sun in Sagittarius means I love travel, philosophy, and expanding my mind by understanding people, places, and how all of us fit together in the world. My moon in Taurus means that I feel better buying or having "things"--meaning, if I'm sad (or if you're sad), I'm probably going to suggest we go grab an ice cream cone and browse the internet to do a bit of clothes shopping. Being a Rising Scorpio means I often come across as a secret-keeper to people who don't know me well--I attribute me being a Rising Scorpio as to why strangers always like to tell me their darkest secrets.
The shape of my chart is important and means something. The way the planets are positioned to each other (transits!) and the signs (and houses) they affect mean something. The amount of signs I have in specific elements (fire, air, earth, wind), qualities (cardinal, fixed, mutable), and yin + yang (earth/water vs. fire/air) all are important and mean something. There's so much that goes into Astrology (it's ridiculous) and anyone that studies it has put in a lot of time and work into their practice. So don't totally knock it until you've tried it. If you're interested in a reading, I offer them online on my store. Feel free to ask any additional questions in the comments below!