Why is there only 12 constellation? Aren't there many constellations in astronomy?

The twelve constellations have a special position.

In astronomy, the orbit of the sun around the earth with the earth as the center is called the ecliptic. The ecliptic plane includes the orbits of all planets except Pluto, as well as constellations. If you divide every 30 degrees, there is exactly one constellation in each interval, totaling twelve constellations, which is also commonly known as the "zodiac".

The sun travels around the ecliptic from west to east once a year. In this year, we can see Aries, Taurus, Gemini, Cancer, Leo, Virgo, Libra, Scorpio, Sagittarius, Capricorn, Aquarius and Pisces at one time, because they are all located in a belt on both sides of the ecliptic.

The "Zodiac" is different from the twelve constellations mentioned above. They refer to the position of the sun in the ecliptic. To put it bluntly, the object of observation is different. Also, people often judge constellations according to the date of birth, and the order and time of constellations come from this. The sun will enter Aries Palace at the vernal equinox every year, stay for one month and then enter Taurus Palace, and so on. This is the origin of constellation time.

Also, the twelve constellations are the main objects of astronomical observation in ancient westerners. By observing the twelve constellations, we can judge the season and farming season, which is somewhat similar to the twenty-four solar terms in China.

The Ps: 12 constellation is just an abbreviation.