Final answer:
Active galaxies appear 'active' due to strong activity in their nuclei caused by the presence of a supermassive black hole. The Milky Way is not an active galaxy because it does not exhibit the same level of central activity.
Step-by-step explanation:
An active galaxy is one that exhibits strong activity in its nuclei, producing a large amount of energy in a small space. This activity is typically caused by the presence of a supermassive black hole at the center of the galaxy. The black hole's gravitational pull draws in surrounding matter, forming an accretion disk where the matter is heated and emits tremendous amounts of radiation. This radiation is what makes active galaxies appear 'active'.
The Milky Way, on the other hand, is not considered an active galaxy because it does not exhibit the same level of central activity as active galaxies. While the Milky Way does have a supermassive black hole at its center, known as Sagittarius A*, it is not actively accreting matter and producing significant amounts of energy. Therefore, it does not emit the same intense radiation as active galaxies.