To make matters even more complicated, constellations are not all the same size and shape, unlike astrological signs. For the most part, the stars that make up a constellation are not physically related, and they’re based on patterns that our forefathers noticed as they looked up at the sky, trying to make sense of it all.

Union of Astronomers

The International Astronomical Union (IAU) formalised the constellations as sky regions, not just star patterns, in 1930. They established the boundaries we use today as a result of this. These modern constellations are based on those introduced by Greek astronomer Ptolemy in the second century CE. He, in turn, took them from Babylonian texts dating back thousands of years. Different cultures have seen patterns in the sky unique to their history. Many cultures share some constellations (Orion is a notable example), but most don’t.

With the current boundaries, 13 constellations lie along the sun’s path. The extra one not listed in any horoscope is Ophiuchus, the Serpent Bearer, which sits between Sagittarius and Scorpius. Whereas the signs remain fixed relative to the solstices and equinoxes, the solstices and equinoxes drift westward close to the constellations or backdrop stars.

While the zodiac may not be a great predictor of love, fortune, and health, it is a great tool for better understanding the motions of the sun, the Earth, and even the cultures that have come and gone on our little planet. The zodiac signs, drawn from constellations that line the course of the sun in the sky, trace Earth’s orbit and wobble and serve as a reminder of astronomy’s modest beginnings.


The sun is in the middle of a wide white oval surrounded by the zodiac signs (in blue). An oval depicting Earth’s orbit and the months of March, June, September, and December is also shown.

Stars surround us, yet some stand out more than others. Because the Earth rounds the sun in a flat plane, we watch the sunset behind the same stars — the zodiac constellations – at regular intervals.

Bottom line: While you may identify the term zodiac with astrology, it also has a prestigious role in astronomy. The 12 constellations that make up the zodiac are located along with the sun’s yearly motion across the sky.