Time-lapse photography is a cinematography technique whereby the frequency at which film frames are captured (the frame rate) is much lower than that which will be used to play the sequence back. When replayed at normal speed, time appears to be moving faster and thus lapsing. For example, an image of a scene may be captured once every second, and then played back at 30 frames per second; the result would be an apparent increase of speed by 30 times. Time-lapse photography can be considered to be the opposite of high speed photography.
Processes that would normally appear subtle to the human eye, such as the motion of the sun and stars in the sky, become very pronounced. Time-lapse is the extreme version of the cinematography technique of undercranking, and can be confused with stop motion animation.
An external webcam is recommended for time lapse videos because it is easier to keep it still. Also, it is much easier to place it at a location from where a wider frame can be captured — larger coverage would result in capturing of more movements, which in turn will make the video look good. It's important that the laptop (or webcam) is kept perfectly still and that it receives constant power. After that, it's just a matter of setting the time interval and recording the time lapse.