September 3, 2005
Clouds are made up of many small droplets of water or ice crystals. Clouds form around what is called a condensation nucleus, which might be a small particle of dust, ash, or smoke. Clouds reflect all visible wavelengths of sunlight, which often makes appear white. However, clouds sometimes appear gray or even black, as they do in this image. This is caused by the process of accumulation, where droplets within the cloud merge with others, forming larger droplets. The space between droplets then becomes larger, allowing more light to be absorbed within the cloud, making it appear darker to the naked eye. The clouds visible in this image demonstrate a fractal pattern. Although clouds look very irregular in shape, they exhibit â€œself-similarityâ€, meaning that their structure looks similar when viewing it very close or very far away. This makes the determination of cloud size very difficult without an exterior frame of reference, such as the coastline of the Baja Peninsula seen here.