046.2 Interpreting the diagram
Objects in the upper right of the HR diagram are bright, but have low surface temperatures. The only way that this is possible is if their surface areas are very large. Thus, these are "giant objects". Because they are red in color, they are called "Red Giants".
Betelguese (the upper-left star in the constellation Orion) is an example of a red-giant star.
Objects in the lower left of the HR diagram are very hot objects which are also very dim. That situation can only happen if they have very small surface area. Thus, these are "dwarfs".
The white dwarf companion Sirius B of the bright star Sirius is an example. Sirius is often called the "Dog Star" and its companion, accordingly, is called 'The Pup'.