The sky has 88 constellations
The International Astronomical Union (IAU) settled the list of constellations in 1922 and officially adopted their boundaries in 1928 (drawn by Belgian astronomer Eugène Delporte and published in 1930). Today a constellation is not a stick figure but one of 88 regions that tile the whole sky. Every point in the sky belongs to exactly one of them.
Some famous shapes are not official constellations at all. The Big Dipper is part of Ursa Major, and the Summer Triangle joins bright stars from three different constellations. Shapes like these are called asterisms.
Why the zodiac has 12
Over a year the Sun appears to travel once around the sky against the stars. That path is the ecliptic. Ancient astronomers cut it into twelve equal 30-degree slices and named each slice after a nearby constellation. Those slices are the zodiac signs.
| Astronomical constellations | Zodiac signs | |
|---|---|---|
| How many | 88 | 12 |
| What they are | Regions of the sky (IAU boundaries) | Equal 30-degree slices of the ecliptic |
| Size | Every region is different | All the same size |
| Used for | Addresses for objects in the sky | Astrology, horoscopes, birthday fun |
The Ophiuchus story
Using the real IAU boundaries, the Sun also passes through Ophiuchus, the Serpent Bearer, between Scorpius and Sagittarius. EarthSky puts the Sun in front of Ophiuchus from about November 30 to December 18 each year. That’s where the “13th sign” headlines come from, but the zodiac was never meant to follow constellation borders; it is a different system.
Why the dates drift
Earth’s axis slowly wobbles, an effect called precession. According to EarthSky, the December solstice point moves about one degree westward against the stars roughly every 72 years. The zodiac dates were set over two thousand years ago, so on your birthday the Sun is often in front of a different constellation from your sign.
A third kind: one made from your name
If you’d like a constellation that is neither one of the 88 nor one of the 12, the Android app "My Constellation" is one way to get it. It turns your name and date of birth into a star layout, connecting lines and a name. It is a creative keepsake, not an official constellation.
The sample name and journal text in these screenshots were typed in Korean; the app itself runs fully in English.
Enter your name and birthday
On the first tab, My Sky, fill in Find Your Constellation with a name and date of birth and your constellation rises in the night sky.
Read what it means
Scroll down for the constellation’s name, element, guardian star, lucky number, nature and rarity grade.
FAQ
Which constellations are the largest and smallest?
By area, Hydra is the largest and Crux, the Southern Cross, is the smallest.
So should I change my zodiac sign?
There’s no need. Zodiac signs are a cultural convention, not an observation. It’s just worth knowing they no longer match the real sky.
My Constellation - Star Sign
One constellation drawn from your name and birthday. No sign-up, fully offline, free on Android.