Fog covering a city overhead.Most people think of fog as a cloud low to the ground that impairs our visibility, but it is actually more complex than you would think. Fog is made up of condensed droplets of water suspended in the air to create a cloud like appearance. However, fog is more common during Autumn nights or dawn. Fog is caused by water droplets from cooled air that can no longer be held (within the air) and are released into the atmosphere.
Fog can have a variety of altitudes from very low to the ground to the as high as the tops of skyscrapers.
Information:
http://www.weatherquestions.com/What_causes_fog.htm
http://www.farmersalmanac.com/weather/a/fog_facts
Pictures:
http://images2.sina.com/english/china/p/2009/0211/U102P200T1D217795F10DT20090211182505.jpg First picture
http://www.stuffintheair.com/images/fog.jpg Second picture
