Most of us, even those who are not so familiar with astronomy or astrology, know about the 12 zodiac constellations and the 12 corresponding zodiac signs. But some sources claim there are 13 of them or even more. This article explains why there is such inconsistency in numbers and how the zodiac signs differ from the zodiac constellations.
History of the zodiac
The word zodiac derives from a Greek phrase meaning “animal circle,” but it’s initially the Babylonian concept, created in the 5th century B.C. Babylonian astronomers divided the band of the sky where the Sun, Moon, and planets move into equal 12 segments, each occupying 30° of celestial longitude. The segments denoted the 12 equal 30-day months and were given the names we now know as “the zodiac signs.”
The constellations along the path of the Sun, Moon, and planets on the sky had been observed even earlier. The first mentions of them belong to ancient Babylonia around 1000 B.C. They only roughly corresponded with the twelve segments of the zodiac. Still, the twelve of these constellations were given the same names as the zodiac signs. The translated names of the zodiac signs and constellations survived through the works of Greek astrologers and astronomers, one of whom was Claudius Ptolemy. In the 2nd century B.C., he wrote Tetrabiblos, which served as the basis for the western zodiac astrology.
The zodiac was mainly an astrological concept until the heliocentric model appeared. Ancient people thought all sky objects spun around the Earth, so it seemed obvious that the cosmic forces focused on human beings. Only in the 17th century, when the telescope was invented, and people realized that the Earth orbits the Sun and they are not the center of the Universe, the astronomical observations of the zodiac constellations became more respected.
What are the zodiac signs?
The zodiac signs are the twelve 30° sections of the zodiac created in analogy with the ancient “ideal year” with equal 30-day months. Most signs refer to living things, the only exception is Libra, the Scales. In modern western astrology, the zodiac signs are supposed to affect human life somehow.
What are the zodiac constellations?
The zodiac constellations are the constellations that are located along the path of the Sun in the sky and roughly correspond to the traditional zodiac signs. The zodiac constellations, even though they are historically connected to astrology, now are as valuable for astronomical observations.
How many constellations are there in the zodiac?
For more than 10 years the hype around the zodiac constellations’ number hasn’t dropped. Some say there are 13 of these constellations or even more than 20. What causes the disagreement? Let’s clarify it.
12 zodiac constellations
There are twelve constellations that roughly correspond to the traditional zodiac signs and are recognized as members of the zodiac family. These are:
They are called “zodiac” on behalf of tradition. Beyond that, there is no reason why they are grouped this way. Let’s see what constellations are overlooked.
13 ecliptic constellations
Astrologers say that during the dates of a zodiac sign the Sun is “in” the corresponding constellation. There are 13 constellations in the sky the Sun regularly visits over a year: Capricornus, Aquarius, Pisces, Aries, Taurus, Gemini, Cancer, Leo, Virgo, Libra, Scorpius, Sagittarius, and Ophiuchus. The last one doesn’t have its traditional zodiac sign, but why? To find this out, we would have to ask the Babylonians.
Babylonian astronomers designated the 12 zodiac signs in the 5th century B.C. They knew the 13th constellation Ophiuchus, but it didn’t fit into the ancient calendar of 12 lunar months. So, Babylonians omitted Ophiuchus for convenience. Modern western zodiac astrology still follows the Babylonian tradition. Moreover, astronomy constellation maps don’t include Ophiuchus in the zodiac family either — it belongs to the Hercules one.
Altogether the 13 constellations are called the constellations of the ecliptic. The ecliptic refers to the imaginary plane containing the Earth’s orbit around the Sun. We from the Earth observe it as the Sun’s path on the sky throughout the year. Over a year, the Sun appears to regularly pass in front of the ecliptic constellations one by one. The entry and exit dates almost perfectly repeat. For Ophiuchus, these dates are November 30 to December 17 (the beginning and the ending may vary by day, depending on the year and your timezone).
Therefore, if you are born at the beginning of December, don’t be surprised that the Sun is “in” Ophiuchus and not the constellation Sagittarius.
25 constellations in the zodiac belt
There is another reason to be surprised about the zodiac. Let’s forget about the tradition and assume that the zodiac constellations are the constellations located in the zodiac. In that case, we’ll get 25 of them! Here is why.
The zodiac, by the standard definition, is the band of the sky where the Sun, Moon, and planets of the Solar System move. It occupies approximately 8° on either side of the ecliptic plane. The number of constellations within 8° on either side of the ecliptic includes Cetus, Corvus, Crater, Hydra, Orion, Pegasus, Scutum, Sextans, Auriga, Canis Minor, Serpens, and Aquila. There are 25 of them in all. How many of these names you’ve even heard?
But the Sun only passes through the 13 ecliptic constellations. Only the Moon and planets meet the extra ones. And, sure enough, they don’t have corresponding zodiac signs.
Still, the traditional definition of the zodiac is convenient because we can refer to the same constellations in a historical and astronomical context. By this definition, the zodiac constellations are the 12 ecliptic constellations that roughly correspond to the traditional zodiac signs.
What is the difference between a zodiac sign and a zodiac constellation?
Zodiac signs and constellations are historically connected but aren’t the same. To say the least, there is a slight difference in their names: the zodiac signs Scorpio and Capricorn correspond to the constellations Scorpius and Capricornus. Even though their names sound similar, they differ as much as astronomy differs from astrology. Here are the main issues that they don’t agree on.
Telling fortunes vs. finding planets
Zodiac signs are now only used in astrology to tell fortunes and describe people’s characters. The zodiac constellations are the subject of astronomy. Formerly they marked the passage of time and the seasons for ancient people and helped create calendars. Even now, they are used for marine navigation and astronomical observations. For instance, they are especially useful for amateur astronomers as reference points to locate planets.
Equal sections vs. different sizes
Zodiac signs divide the zodiac band of the sky into equal 30° sections and represent the equal 30-day months. But the actual constellations are of different sizes and shapes. For example, the constellation Scorpius covers an area of 497 square degrees, and the Sun passes through it only for about 7 days. And the constellation Virgo occupies 1,294 square degrees, and the Sun spends around 45 days in front of it.
Fixed ancient dates vs. real astronomical dates
The zodiac signs’ dates are now about a month ahead of when the Sun meets the corresponding constellations. These dates were established more than two thousand years ago, but today things changed. For example, Aries now meets the Sun around April 19 (the exact date depends on the year and your timezone) instead of the astrological date of March 21. So, most people who think of themselves as Aries were born when the Sun was in Pisces.
The reason for this time shift is the axial precession of the Earth. Our planet is like a spinning top: it’s flattened at the poles and bulges at the equator, pulled by the Moon and Sun. So, it wobbles as it spins, tracing a cone of 23.5° radius with its axis. The wobble is called the precession of the Earth’s axis, or the precession of the equinoxes. Each spin lasts one day, but each gyration around the cone takes 25 800 years. The movement slowly alters the view of the zodiac from the Earth, making the constellations appear to slide to the east about 1° per human lifetime.
Moreover, just as in ancient times, now the Sun passes through the 13th constellation Ophiuchus that we mentioned above. So, no zodiac constellation meets the Sun from around November 30 to December 17, but, in astrology, these days belong to the sign Sagittarius.
It’s the astronomical view of things. Astrologers defend themselves by saying that they use the tropical zodiac, which is fixed to seasons, not the position of constellations. So, it’s your choice to believe whether you are Aries or Pisces, Sagittarius or Ophiuchus.
Where was the Sun when you were born?
Here we provide the astronomical dates when the Sun passes through the ecliptic constellations nowadays; the beginnings and endings may vary by a day, depending on the year and your timezone:
- Aries: April 19 — May 13;
- Taurus: May 14 — June 19;
- Gemini: June 20 — July 20;
- Cancer: July 21 — August 9;
- Leo: August 10 — September 15;
- Virgo: September 16 — October 30;
- Libra: October 31 — November 22;
- Scorpius: November 23 — November 29;
- Ophiuchus: November 30 — December 17;
- Sagittarius: December 18 — January 18;
- Capricornus: January 19 — February 15;
- Aquarius: February 16 — March 11;
- Pisces: March 12 — April 18.
Do astronomy apps show the zodiac constellations accurately?
Some users complain that Star Walk 2 and Sky Tonight apps show the incorrect positions of the zodiac constellations. For example, during the astrological dates of the zodiac sign Sagittarius, the apps show that the Sun meets Scorpius or even the 13th constellation Ophiuchus. Now you know that the zodiac signs’ dates don’t tightly correspond with the constellations’ real position in the sky. The dates used in the astronomy apps are not imagined but accurately calculated so that you can see what’s in the sky above you now. Try using Star Walk 2 or Sky Tonight to learn what zodiac constellations are visible this evening. Stargazing is no less fun than reading horoscopes!
Which zodiac constellation is the largest?
Virgo is the largest zodiac constellation and the second-largest constellation in the whole sky, after Hydra. The constellation Virgo covers 1,294 square degrees of the sky. It’s seen from November to August in both hemispheres, from latitudes between -80° to +80°. To easily find Virgo in the night sky from your location, use the stargazing app Star Walk 2.
Where are the zodiac constellations located?
The zodiac constellations are located along the Sun’s path in the sky throughout the year. To find them at night, look along the approximate path that the Sun follows during the day — from east to west across the sky. Note that you won’t see the zodiac constellation that is currently behind the Sun. Use the astronomy app Sky Tonight to locate all of the zodiac constellations.
How many constellations are on the ecliptic?
There are 13 constellations on the ecliptic: Aries, Taurus, Gemini, Cancer, Leo, Virgo, Libra, Scorpius, Ophiuchus, Sagittarius, Capricornus, Aquarius, and Pisces. The 12 of them (except for Ophiuchus) are also called zodiac constellations. Test your knowledge of the constellations with this quiz!
What is zodiacal light?
Zodiacal light is a hazy pyramid of light extending up from the horizon and centered on the ecliptic. Zodiacal light isn’t connected to the zodiac constellations but to the band of the sky where we see them. This rare celestial event can be observed in spring and fall. Read more about the zodiacal light in our article.
Bottom line: There are 12 constellations that are traditionally called “zodiac constellations.” They are historically connected to the zodiac signs, but over the course of time, the functions of them divided. The zodiac signs now are only used in astrological horoscopes that may be fun to read but aren’t scientifically based. The zodiac constellations, on the other hand, are real groups of stars you can observe for yourself. They are explored by astronomers and can be used to locate planets and other celestial objects.
Text Credit: Vito Technology, Inc.