How is the zodiac defined in astronomy?

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 the same as those of the 12 constellation near the ecliptic, namely Aries, Taurus, Gemini, Cancer, Lion, Virgo, Libra, Scorpio, Sagittarius, Capricorn, Aquarius and Pisces. 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 Pisces Palace. Around June 22, I came to the summer solstice and entered the twin uterus; On September 2 1 day, I came to the autumnal equinox and entered the virgin palace. 65438+Come to the winter solstice around February 22nd and enter the Sagittarius 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. The first house "Life Palace", also known as "Ascending Palace", was originally the fixed position of Aries. The first house represents the birth of life-"I am", showing a person's character, words and deeds, health, appearance, body shape and the first impression. In modern astrology, the first house represents the people's palace. Center position: right ascension 2: 40, declination 2 1. Between Pisces and Taurus. α, β and γ (Building 3, Building 1 and Building 2) are about 20 degrees south of Andromeda γ. α is a second-class star, which forms an isosceles triangle with Andromeda β and γ. There are five stars above level 4 in the constellation. The first house of the zodiac, with longitude ranging from 0 degrees to 30 degrees, was originally in Aries, hence its name. But due to precession, it has now moved to Pisces. On March 2 1 every year, the sun comes to this house, and the solar term is the vernal equinox, so the vernal equinox is also called "the first point of Aries Palace". The second house, Caibo Palace, was originally a fixed position of Taurus. Represents a person's material and resources-"I own", showing a person's economic situation, money values, ability to deal with property, resources and so on. In modern astrology, the second house represents the "economic house". Center position: 4: 20 right ascension, declination 17 degrees. In the south of Perseus and the Imperial Palace. North of Orion. There are the famous Pleiades and Pleiades star clusters in the constellation. Alpha is an orange 1 equal star. There are 28 stars in the constellation that are brighter than 4. Jinniu Palace is the second palace, and the longitude of the Yellow River ranges from 30 degrees to 60 degrees. Every year around April 20th, the sun will come to this house. At that time, the solar term was "Brother Palace", the third house in Grain Rain, which was originally the fixed position of Gemini. It represents a person's environment, showing a person's learning ability (especially before college), communication skills, short trips, and friends who can't choose-meaning brothers and sisters, relatives and neighbors. In modern astrology, the third house represents the "news house". Center position: 7: 00 right ascension, 10 minute, 24 degrees right ascension. Between Taurus and Cancer. The two brightest stars, α and β, stand out. α is a second-order star and β is a 1 order star. The open cluster M35 is visible to the naked eye. There are 19 stars brighter than 4 in the constellation. Double uterus, third house. The longitude of the yellow meridian ranges from 60 degrees to 90 degrees. Every year the sun comes to this palace around 2 1, when the solar terms are full. The fourth house "Tianzhai Palace" was originally the fixed position of cancer. It represents a person's inner feelings and family, showing a person's family and clan, subconscious, old age, grave, and wealth such as inheritance and real estate. In current astrology, the fourth house represents the real estate house. Center position: 8: 00 right ascension, 10 minute, 20 degrees right ascension. Gemini East, Leo West. There are four brighter stars in the constellation, and there is an open cluster M44 (Ghost Cluster). The fourth house of Cancer Palace. The longitude of the Yellow River varies from 90 degrees to 120 degrees. It originally came from Cancer, hence its name. Every year around June 22nd, the sun comes to this palace. At this time, the solar term is the summer solstice, so the summer point is also called "the first point of Cancer Palace". The fifth house, Daughter's Palace, was originally the fixed position of Leo. The fifth house represents a person's attitude and expression of feelings, showing a person's love, children, gambling, leisure and entertainment, as well as his talent and creative ability in art and literature. Because it is related to pure happiness, it stands for "Palace of Entertainment" in current astrology. Center position: right ascension 10: 30, declination 16 degrees. Cancer is in the east, virgins and latecomers are in the west.