Dense fog over the Gangetic plains of the Indian Subcontinent, with the Himalayas to the north and the Bay of Bengal at bottom right, as imaged by a NASA satellite on 23 December 2012. Fog is a collection of liquid water droplets or ice crystals suspended in the air at or near the Earth's surface; it is closer to the Earth's surface than clouds and denser than mist.Photo: NASA Earth Data - LANCE Web Mapping Service, MODIS Rapid Response System