The position and motion characteristics of celestial bodies on the celestial sphere

The position and motion characteristics of celestial bodies on the celestial sphere are that almost all stars rotate around the polar axis.

How to determine the position of a celestial body?

Basic knowledge of astronomy

Naming rules of stars in 1. constellation

The naming rules of the stars in the constellation are as follows: according to the brightness of each star, from bright to dark, each star is represented by a Greek letter. When all 24 Greek letters are used up, they are represented by Arabic numerals.

2. The concept of "quantity"

"Magnitude" is a representation of the brightness of stars in astronomy, which is recorded as m. Astronomy stipulates that the brightness of stars is always represented by magnitude. The smaller the magnitude, the brighter the star. For every phase difference of 1 magnitude, the brightness difference of stars is about 2.5 times. The darkest star we can see with the naked eye is a 6-magnitude star (6-meter star).

The brightness in the sky is above 6 (that is, the magnitude is less than 6), which means we can see more than 6,000 stars. Of course, I can only see half of it every night, more than 3000. At the full moon, the brightness of the moon is equivalent to-12.6 (astronomy says-12.6m).

The sun is the brightest celestial body we have ever seen, with a brightness of-26.7 m; Today, the world's largest astronomical telescope can see objects 24 meters deep. The magnitude we are talking about here actually reflects the brightness of celestial bodies "seen" from the earth, which is called "apparent magnitude" in astronomy.

The sun looks brighter than all the stars, its apparent magnitude is much smaller than all the stars, and it is only touched by its light when it is close to the earth. What's more, like the moon, it doesn't shine at all, but reflects some sunlight, making it the second brightest celestial body in people's eyes. There is also a concept of "absolute magnitude" in astronomy, which truly reflects the actual luminous ability of stars.

3. The concept of "celestial sphere"

In astronomy, in order to adapt to people's intuitive feelings, the sky is assumed to be a huge spherical surface, that is, the celestial sphere. The center of the celestial sphere is naturally our earth, and its radius is infinite. The celestial sphere is just a hypothesis, an "ideal model". The concept of celestial sphere is introduced only to determine the position of celestial bodies and other needs.

4. Concepts of "celestial equator" and "celestial pole"

In astronomy, the method of determining the position of celestial bodies is very similar to the earth's surface, and it is also realized by latitude and longitude coordinate system. The most commonly used and important celestial coordinate system is the equatorial coordinate system.

The intersection of the earth's equator plane and the celestial sphere is a great circle, which is called "celestial equator" and is the projection of the equator on the celestial sphere; The straight line extending infinitely in the north-south direction of the earth's rotation axis forms two intersections with the celestial sphere, which are called the north celestial pole and the south celestial pole respectively. The celestial equator and celestial pole are the benchmarks of the celestial equator coordinate system.

5. Zodiac and Zodiac Constellation

The apparent motion of the sun on the celestial sphere can be divided into two situations, namely, Sunday apparent motion and annual apparent motion. "Annual apparent motion" refers to the phenomenon that the earth's revolution causes the sun to "cross" between constellations.

Astronomy calls the annual orbit of the sun on the celestial sphere "ecliptic", which is the projection of the earth's orbital plane on the celestial sphere. The sun rotates once a year on the celestial sphere along the ecliptic. In order to determine the position, people divide the ecliptic into twelve equal parts (each part is equivalent to 30 parts), and each part is named after an adjacent constellation. These constellations are called the zodiac or the zodiac.

This is equivalent to dividing a year into twelve segments, in which the sun enters a constellation. In the west, when a person is born, which constellation the sun is going to, he is said to belong to this constellation.

Because we can only see the sun during the day, we can't see the stars at this time, that is, we can't see the constellation where the sun goes. In other words, on our birthday, we just can't see our horoscope.