Webcams are made to capture video at 15-30 frames per second (fps). Normally these files are saved in a movie file in a .mov, .wmv, or .mpeg file format. When viewed in a player these frames are shown one after the other so that the motion that was capture is played back at the same speed.
When it is dark, as in the case when shooting the night sky, there are less photons reaching the chip inside the web cam so in movie mode your computer screen will be completely black.
This is where video integration comes to the rescue. Instead of storing and presenting the frames captured by you video camera on after another, video integration software stacks the frames on top of each other. The light collected from one frame is added to the light collected from the next frame. The more frames you stack, the brighter the objects being captured become. This is because the photons hitting the camera chip in the next frame are added to those collected in the previous frame.
You can put a web cam in a dark room in your house and connect it to you computer running video integration software. After you will begin to see a chair or table start to appear. Wait a little longer and you will start to see more detail in the image.The same holds true if you attach the camera to you telescope and point it at a deep space object, say the ring nebula, and collect the light for a period of time. Because of another component of webcam capture software called drift integration you do not even have to track the object as accurately as with film based astrophotography.