Related topics: climate change · earth · climate models · climate · sunlight

How trees influence cloud formation

As part of the international CLOUD project at the nuclear research center CERN, researchers at PSI have identified so-called sesquiterpenes—gaseous hydrocarbons that are released by plants—as being a major factor in cloud ...

Webb reveals new structures within iconic supernova

NASA's James Webb Space Telescope has begun the study of one of the most renowned supernovae, SN 1987A (Supernova 1987A). Located 168,000 light-years away in the Large Magellanic Cloud, SN 1987A has been a target of intense ...


A cloud is a visible mass of droplets or frozen crystals suspended in the atmosphere above the surface of the Earth or another planetary body. A cloud is also a visible mass attracted by gravity, such as masses of material in space called interstellar clouds and nebulae. Clouds are studied in the nephology or cloud physics branch of meteorology.

On Earth the condensing substance is typically water vapor, which forms small droplets or ice crystals, typically 0.01 mm in diameter. When surrounded by billions of other droplets or crystals they become visible as clouds. Dense deep clouds exhibit a high reflectance (70% to 95%) throughout the visible range of wavelengths. They thus appear white, at least from the top. Cloud droplets tend to scatter light efficiently, so that the intensity of the solar radiation decreases with depth into the gases, hence the gray or even sometimes dark appearance at the base. Thin clouds may appear to have acquired the color of their environment or background and clouds illuminated by non-white light, such as during sunrise or sunset, may appear colored accordingly. In the near-infrared range, clouds look darker because the water that constitutes the cloud droplets strongly absorbs solar radiation at those wavelengths.

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