cloud

In meteorology, a cloud is an aerosol consisting of a visible mass of minute liquid droplets, frozen crystals, or other particles suspended in the atmosphere of a planetary body or similar space. An aseosol is a suspension of fine solid or liquid particles in gas. Smoke, fog, and mist are aerosols. Water or various other chemicals may compose the droplets and crystals. On Earth, clouds are formed as a result of saturation [the degree to which sth has been mixed into sth else] of the air when it is cooled to its dew point, or when it gains sufficient moisture (usually in the form of water vapor) from an adjacent source to raise the dew point to the ambient [surrounding] temperature.

They are seen in the Earth’s homosphere, which includes the troposphere, stratosphere, and mesosphere. Nephology is the science of clouds, which is undertaken in the cloud physics branch of meteorology. 它们出现在地球的均质层，包括对流层、平流层和中层。云学是气象学的云物理学分支中研究云的科学。

The word Sapien derives (or comes) from an old latin word meaning ‘Wise’. The word ‘Sapien’ is most commonly recognized when used in conjunction with the word ‘Homo’ (an anient greek word meaning ‘same, or man’). Used together and written as ‘Homo sapien’, it describes a species of man or human being.

The two biggest reasons that clouds stay in the sky are: 1) small drops, and 2) wind. Small drops of water fall more slowly than big drops. The reason is that as drops fall through the air, the air pushes back on them. Because small drops have less mass and more surface area than large drops, they have a harder time pushing the air out of the way.

Tropospheric clouds can have a direct effect on climate change on Earth. They may reflect incoming rays from the sun which can contribute to a cooling effect where and when these clouds occur, or trap longer wave radiation that reflects back up from the Earth’s surface which can cause a warming effect. The altitude, form, and thickness of the clouds are the main factors that affect the local heating or cooling of Earth and the atmosphere. Clouds that form above the troposphere are too scarce and too thin to have any influence on climate change. Clouds are the main uncertainty in climate sensitivity.

The origin of the term “cloud” can be found in the Old English words clud or clod, meaning a hill or a mass of rock. Around the beginning of the 13th century, the word came to be used as a metaphor for rain clouds, because of the similarity in appearance between a mass of rock and cumulus heap cloud. Over time, the metaphoric usage of the word supplanted the Old English weolcan, which had been the literal term for clouds in general.

Clouds play an important role in various cultures and religious traditions. In China, clouds are symbols of luck and happiness. Overlapping clouds are thought to imply eternal happiness and clouds of different colors are said to indicate “multiplied blessings”.

“祥云”图案最早出现在周代中晚期的楚地。祥云纹寓意祥瑞之云气，表达了吉祥、喜庆、幸福的愿望以及对生命的美好向往。

六级/考研单词: liquid, freeze, crystal, particle, suspend, planet, haze, mist, compose, saturate, dew, suffice, adjacent, undertake, physics, derive, wise, conjunction, outgoing, ray, trap, radiate, altitude, affection, scarce, uncertain, metaphor, heap, usage, literal, secular, overlap, implicit, eternal