Is astrology scientific？ Find your constellation in the night sky.

　　Astronomy around us

　　No matter how much you know about astronomy, you probably know what your "constellation" is. At present, the International Astronomical Union accurately divides the whole day into 88 constellations, of which 12 are called the zodiac constellations and are associated with the date of birth. Do you know how your constellation is determined? And is it scientific to link the date of birth with the constellation and infer people’s fate?

　　The zodiac determined by the sun

　　Because the earth revolves around the sun once a year, we will see the sun walking through the sky full of stars, once a year, and again. In order to record the position of the planet in the starry sky, the Babylonians recorded the trajectory of the sun in the starry sky — — The ecliptic is divided into 12 segments, and according to the shape arrangement of some brighter planets in each segment, they are named by the images in myths and legends, namely, Aries, Taurus, Gemini and other twelve constellations, and each constellation is assigned a unique symbol. After that, when they observe the positions of Mercury, Venus, Mars, Jupiter and Saturn visible to the naked eye in the starry sky, they only need to record the time and the constellation symbols where the planets are.

　　The way to divide people’s constellations according to their birthdays is similar. For example, you were born in early June and belong to Gemini, because in early June, the sun was just near Gemini, the zodiac sign.

　　Apparent motion of stars determined by earth’s revolution and rotation

　　However, it is not realistic to see the constellation you belong to on your birthday. For example, people born in early June are classified as Gemini, but really enjoying Gemini in the night sky will have to wait until winter.

　　Maybe you have realized what the problem is. Because the sun shines brightly, the constellation where the sun is located is just covered by its light, so when the sun passes through which constellation, we just can’t see it at that time. To enjoy this constellation well, we can only wait for it to appear in the night sky after half a year away from the sun.

　　Although stars and planets are at different distances from us, in the starry sky at night, they all seem to be on the same huge spherical shell. This imaginary ball is called the celestial sphere. Seen from the earth, the movement of the sun on the celestial sphere, that is, the apparent movement of the sun in the sky in astronomy, can be divided into two situations. One is that the sun rises in the east every morning, reaches the farthest position from the horizon at noon and sets in the west in the evening. This visual effect caused by the earth’s rotation from west to east is called Sunday apparent motion. The other is that in a year’s time, the sun passes through the constellations in the sky and finally returns to the starting point, which is called the annual visual movement. This is caused by the revolution of the earth.

　　The sun’s Sunday apparent motion and annual apparent motion are superimposed, which causes the stars to rise and set in the west every night, but the stars that rise every day are different, and they also rotate once a year on the celestial sphere. The zodiac sign on the celestial sphere, which is with the sun, will be at the other end of the connection between the sun and the earth in half a year, hanging high above your head at midnight.

　　Due to the shape of the earth itself and the gravitational effect of the sun and the moon on the earth, there is still a slow change in the direction of the earth’s rotation axis. The movement of the earth’s axis, called precession, is similar to that of a falling gyro. When the gyro itself is still rotating, the direction of the gyro axis is also circling. It takes about 26,000 years for the earth’s axis to rotate once, so it may be difficult to feel the existence of precession through the naked eye in a person’s life. However, thousands of years have passed since the Babylonians lived, and the effect of precession is highlighted: the actual position of the sun in the celestial sphere and the definition of the Babylonians have deviated from two constellations.

　　Falsified astrology

　　Although it is simple and easy to use constellations as a tool for astrometry, its accuracy is not high. With the development of astrometry technology, this method is no longer used in subsequent observation and research. However, this once scientific tool has been "carried forward" in the hands of others, and a set of complicated statements has been concocted, which link people’s personality, fate and other signs with constellations. Many people are convinced of these statements, and even use them as guiding ideology in matters that need to be taken seriously, such as personnel arrangement and finding a partner.

　　In 1983, Sean Carlson, a scientist at the University of California, Berkeley, conducted a double-blind experiment in astrology, and published the results in Nature, a top international scientific magazine, in 1958. In the experiment, he invited the best astrology "experts" recommended by astrology circles in the United States, and fully communicated with these astrologers on the experimental methods and obtained their consent. In the first part of the experiment, the experimenter first collected the data of each subject according to the requirements of astrologers. After the astrologers predicted the personality characteristics of each subject according to these data, the experimenter provided each subject with three predictions without signature, one of which was made by the astrologer for the specific subject himself and the other two by the astrologer for other subjects. The subjects scored the degree of consistency between the three predictions and themselves. In the second part of the experiment, each subject obtained his own personality characteristics through the California Personality Scale (CPI). Each astrologer will get three unsigned test results, one for a specific subject and the other two randomly selected. Astrologers need to choose the questionnaire that belongs to that specific subject from these three copies. The test results show that the success rate of astrologers’ prediction is the same as the random probability. In layman’s terms, the success rate is basically the same as relying on "Meng".

　　In other words, it is a good way to find out your own "constellation" according to your date of birth. But I hope to know my future and destiny, and that is modern superstition.

　　(The author is a doctoral student at the National Space Science Center, Chinese Academy of Sciences)

　　(The pictures in this edition are from the Internet except for labeling.)