Transcript: Classification is often an important first step towards physical understanding. Imagine you lived in a small town and did a survey where you gathered information on every inhabitant, three pieces of information: their age, their height, and their weight. If you plotted height against weight you would notice an obvious trend, height and weight are correlated. Most people would fall on a particular track in a diagram of height plotted against weight. Some combinations are never seen; you would not have someone who is 3 feet high and 300 pounds nor someone who is 6 feet high and 60 pounds. The pattern will be telling you something. In this case the pattern reveals age because babies obviously grow into children who grow into larger people, and so height and weight are correlated with age. In the case of stars, a similar situation is applied because astronomers did not know the fundamental nature of stars when they first started observing them, and they used stellar classification to get a start.