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

Hubble sees swirls of forming stars

At around 60 million light-years from Earth, the Great Barred Spiral Galaxy, NGC 1365, is captured beautifully in this image by the NASA/ESA Hubble Space Telescope. Located in the constellation of Fornax (the Furnace), the ...

Gemini South's high-def version of 'A Star is Born'

NASA's James Webb Space Telescope is still more than a year from launching, but the Gemini South telescope in Chile has provided astronomers a glimpse of what the orbiting observatory should deliver.

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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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