This is the first sentence in "Night Mooring at Maple Bridge" by Zhang Ji, a poet of the Tang Dynasty.
The full sentence is: The moon is setting, the crows are crying, the sky is covered with frost, the river maples are fishing and the fire is facing melancholy. Hanshan Temple outside the city of Suzhou, the midnight bells are ringing to the passenger ship
The moon is setting, the crows are crows, and the frost is all over the sky. The moon is falling, which means that the sky is about to break. It is said that the autumn frost is full of frost, which makes people feel chilled to the bone.
Although this poem describes a specific scene, it actually expresses the author's loneliness and a touch of sadness.
It can be interpreted as: The sky is about to break, and the crows have begun to crow. The bone-chilling chill all over the body makes people feel that there is frost in all directions.
At Hanshan Temple outside Gusu City, the bell rang at midnight to reach the passenger ship. It is a popular masterpiece through the ages. The artistic value of "Mooring at Maple Bridge at Night" lies in its depiction of a night mooring with bright colors and blending of scenes, which expresses an unprecedented feeling. It describes the environment of night mooring on the Qiujiang River and the poet's feelings from three aspects: vision, hearing and touch.
Hanshan Temple is located in Fengqiao Town outside Wenwan, Suzhou. It was built in the Liang Tianjian Period of the Six Dynasties (502-519) and has a history of more than 1,400 years. In Liang Dynasty, its original name was "Miao Li Pu Ming Pagoda Courtyard". During the Zhenguan period of the Tang Dynasty, eminent monks Hanshan and Shide from Tiantai Mountain in Zhejiang came here to be the abbots, and the name was changed to "Hanshan Temple".
"The moon sets and the crows cry, and the sky is filled with frost." The waning moon sets in the west, which is depressing; the crows cry sadly, making people cry; the sky is filled with frost and frost, and the cold air is pressing. "The sky is covered with frost" is a strange phrase. Originally, it is a natural phenomenon when autumn frost falls on the ground, causing an awe-inspiring chill. However, in the eyes of the desolate poet, it seems that the sky is covered with frost and the chill is overwhelming. It is quite desolate and depressing. Feeling of coldness. Writing about the thick autumn frost and the miserable cold wind actually conveys the poet's desolate mood. What is particularly harsh is the "crow", which is originally a sinister, ominous and unfavorable omen.
Autumn is cold and frosty, and the night is quiet. So is the phenomenon of "frost-filled sky" reasonable? We have to analyze the causes of frost: in the early morning of the cold season, grass blades and soil clods are often covered with a layer of frost crystals. People often call this phenomenon "frost". In late October every year, there is always the "Frost Descent" solar term. We have seen snowfall and rainfall, but no one has seen frost. In fact, frost does not fall from the sky, but forms in the air near the ground. The formation of frost is not only related to the weather conditions at the time, but also to the properties of the attached objects. When the temperature of the surface of the object is very low, but the temperature of the air near the surface of the object is relatively high, then there is a temperature difference between the air and the surface of the object. If the temperature difference between the surface of the object and the air is mainly caused by radiative cooling of the surface of the object , the air will cool when the warmer air comes into contact with the colder surface, and excess water vapor will precipitate when it reaches water vapor supersaturation. If the temperature is below 0°C, excess water vapor condenses into ice crystals on the surface of the object, which is frost. Frost therefore always forms under weather conditions conducive to radiative cooling of the surface. In addition, clouds hinder the radiative cooling of ground objects at night. Clouds in the sky are not conducive to the formation of frost. Therefore, frost mostly appears on clear nights, when ground radiative cooling is intense. In addition, wind also has an impact on frost formation. When there is a breeze, the air slowly flows across the surface of cold objects, continuously supplying water vapor, which is conducive to the formation of frost. However, when the wind is strong, the air flows very fast and the time it touches the surface of cold objects is too short. At the same time, when the wind is strong, the air in the upper and lower layers easily mix with each other, which is not conducive to lowering the temperature, which will also hinder the formation of frost. Generally speaking, when the wind speed reaches level 3 or above, frost will not easily form.
Therefore, frost generally forms on clear, breezy or windless nights in the cold season. The formation of frost is not only related to the above-mentioned weather conditions, but also related to the properties of ground objects. Frost forms on the surface of an object that is cooled by radiation. The easier it is for the surface to radiate heat and cool quickly, the easier it is for frost to form on it. That is to say, if an object has a relatively large surface area compared to its mass, frost will easily form on it. Grass blades are very light but have a large surface area, so frost easily forms on the grass blades. In addition, objects with rough surfaces are more conducive to radiation and heat dissipation than smooth surfaces, so frost is more likely to form on objects with rough surfaces.
Therefore, from a physical point of view, it is unreasonable to say "the sky is full of frost"