The Unknown in Astronomy

One of the best techniques astronomers employ is in understanding what is normal. For example, if we consider our Sun a normal star, how do other stars compare? When is a star atypical when compared to the Sun? And atypical in what way?

It is usually the abnormal or weird objects that are the most interesting. One example is stars that vary significantly in brightness and energy output on a regular basis. Why do these stars go through these variations? Or consider stars that also vary significantly in brightness and energy output, yet on an irregular basis. What makes them so much different than regular variable stars, or steady stars like our Sun?