The universe we are in has two basic characteristics, namely materiality and motion, that is to say, the universe is composed of matter, and all kinds of matter are aggregated and combined to form a variety of celestial bodies, including stars, planets, asteroids, moons, dwarf planets, comets, black holes, meteoroids, interstellar matter, nebulae and so on. At the same time, all the celestial bodies in the universe are in motion, and these celestial bodies attract and orbit each other, forming a system of celestial bodies nested in each other.
Today is staged the "Mercury Sun" celestial phenomenon
All the celestial bodies that make up our solar system are also in constant motion, and this movement makes us see that the relative position relationship between the celestial bodies on the earth is also constantly changing, thus forming various celestial phenomena. There is a type of celestial phenomenon that occurs between the observer (the Earth), the Sun and other celestial bodies, for example, between the Earth, the Sun and the Moon, there will be a "solar eclipse" and a "lunar eclipse" celestial phenomenon, when the three are connected in a line, and the moon is located between the earth and the sun, a "solar eclipse" celestial phenomenon will be staged; and when the three are connected in a line, and the earth is located between the moon and the sun, a "lunar eclipse" celestial phenomenon will be staged. However, the celestial signs we are talking about today occur between the Earth, the Sun, and the other planets in the solar system.
Schematic diagram of the motion of the planets in the Solar System
If this third object is a planet in the orbit of the Earth, such as Venus and Mercury, we use Mercury as an example to illustrate the relative position relationship between the three. The Earth and Mercury rotate around the Sun according to different rotational periods, first there are two special positions, that is, when the Earth, Mercury and the Sun are connected in a straight line, if Mercury is located between the Earth and the Sun, we are called "Mercury under the union", and at this time, because Mercury is located between the earth and the Sun, mercury can be observed on the earth on the surface of the sun, which is the "Transit of Mercury" phenomenon.
Mercury transit
If the Earth, Mercury, and the Sun are connected in a straight line, if the Sun is between the Earth and Mercury, we are called "Mercury Converging", and at this time, because Mercury is located behind the Sun, we cannot see Mercury on Earth. In fact, today (May 4, 2020) is the "Mercury Conjunction Day", the time is about 5 o'clock, but this is a celestial phenomenon that cannot be appreciated on Earth, so everyone does not have to look up at the sky. We know that Mercury is the closest planet to the Sun, so it is very difficult for us to observe Mercury on Earth, because mercury always has such a huge sun on its edges, and the sun's brilliance will flood Mercury.
Mercury
The best time to observe Mercury in astronomical observations is when we see mercury on Earth at its farthest distance from the Sun, which we call "great distance", when mercury and the Sun have the greatest angular distance. When we observe on Earth, if Mercury is on the west side of the Sun, it is called "Mercury West Macro", at which point we should observe Mercury in the morning when the Sun has not yet risen, and Mercury will appear at dawn at dawn at the eastern low altitude. If Mercury is located on the east side of the Sun, called the "Mercury East Distance", at this time we should observe Mercury after the sun has set in the evening, and Mercury will appear at dusk at low western altitudes.
Schematic diagram of Mercury's eastern distance
In the Solar System, not only Mercury has "lower", "upper", "east and west" celestial phenomena, but also Venus in the earth's orbit. Venus is larger than Mercury and closer to Earth, so Venus is the brightest object seen on Earth besides the Sun and Moon, and when Venus is in a "lower" position, we can see the obvious "transit of Venus" phenomenon. In the same way, when there is a "Great Distance west of Venus", we can see bright Venus in the morning, called "Venus"; when there is a "Venus East Distance", we can see bright Venus in the evening, called "Chang Gung Star".
Schematic diagram of the phase change of Venus