Who can explain why the constellations we usually talk about are all zodiac signs?

The word zodiac comes from the Greek zodiakos, which means zoo. In the eyes of the Greeks, constellations are made up of various animals, which is the origin of the names of the twelve constellations. In astronomy, the orbit of the sun around the earth with the earth as the center is called the ecliptic. The width of the ecliptic is 16 degrees, 360 degrees around the earth. The ecliptic plane includes the orbits of all planets except Pluto, as well as the constellations, exactly every 30 degrees. Each interval has a constellation, a total of twelve constellations, called the "Zodiac".

Division on the ecliptic

The sun runs from west to east on the ecliptic and circles the sky once a year. There are twelve constellations on a belt on both sides of the ecliptic. They are Aries, Taurus, Gemini, Cancer, Leo, Virgo, Libra, Scorpio, Sagittarius, Capricorn, Aquarius and Pisces. People on earth can see them one after another in a year.

Babylonians observed these constellations for a long time, determined the ecliptic through observation, and divided the ecliptic into 12 equal parts, each equal part was 30 degrees, which was called 1 segment. The sun travels around the ecliptic in 12 months/cycle, so it travels on the ecliptic every month 1 segment. In the eyes of the ancients, the sun was Apollo, and its resting place must be a magnificent palace. Therefore, they called the 1 section of the ecliptic 1 palace. In this way, the section 12 on the ecliptic becomes the "zodiac". The names of the zodiac signs are similar to the 12 constellation near the zodiac signs, namely Aries, Taurus, Twin Uterus, Cancer, Lion, Virgo, Libra, Scorpio, Sagittarius, Capricorn, Aquarius and Pisces.

The difference between the zodiac and the zodiac

Although the names of the zodiac signs are the same as those of the 12 constellation near the zodiac signs, they are essentially different. The zodiac indicates the position of the sun on the ecliptic, and the size of each constellation is fixed. It's all 30 degrees, and the time when the sun enters each house is basically fixed. Now the sun comes to the vernal equinox on March 2 1 every year and enters Aries Palace. Around June 22, I came to the summer solstice and entered the Cancer Palace. Before and after September 23, I entered Libra Palace. 65438+came to the winter solstice around February 22 and entered Capricorn Palace.

However, this was not the case before 2000, because under the gravity of the sun and the moon, the rotation axis of the earth did not point to the same position in the sky, but turned around in the sky. This phenomenon is called precession. Due to precession, before 2000, the sun was located in the above four positions of Aries, Cancer, Libra and Capricorn. Different from the ecliptic, the 12 constellation near the ecliptic has different sizes. For example, the width of Pisces is 49 degrees, while the width of Cancer is only 2 1 degree. 12 constellation is not necessarily located on the ecliptic, but distributed within 8 degrees on both sides of the ecliptic.