These images are generated by geostationary satellites orbiting 22,000 miles above the equator looking at the United States. These include visible, infrared and water vapor images. The images are updated once an hour at about 30 after the hour.
This type of image shows heat based radiation from the infrared spectrum. In other words, the warmer the surface, the more infrared radiation it emits. For a satellite image, cooler surfaces are bright and warmer surfaces are dark. Since the atmosphere cools as you increase in altitude, clouds would show up as bright areas and land surfaces as dark areas. In addition, low clouds will be more gray and higher clouds will show up more white. Tall thunderstorm clouds will show up as bright white and fog will be hard to decern from land areas. A large advantage of IR is that you can view it 24 hours a day.
There are 5 sectors for the visible image:
East - GOES east view centered over 75 west longitude showing eastern US and Atlantic Ocean.
West - GOES west view centered over 135 west longitude showing western US and Pacific Ocean.
Hemisphere - this is a pieced/merge view of both the GOES east and GOES west satellite views remapped to a Mercator projection.
US - this is a pieced view of GOES east and west remapped to a polar stereographic projection.
Regional - these are regional views remapped to a polar stereographic projection.