Interpreting the HR Diagram

Look carefully at the diagram. Are all the stars located in one group? Explain you results.

Look at Star A. Describe its temperature:  very cool cool medium fairly hot very hot

Describe its luminosity:  very dim dim medium fairly bright very bright

You described the star as being and

Now look at Stars B through D. Describe each of them, and see if their brightness and temperature meet the expectation.

Star B:  very cool cool medium fairly hot very hot  and  very dim dim medium fairly bright very bright

Star C:  very cool cool medium fairly hot very hot  and  very dim dim medium fairly bright very bright

Star D:  very cool cool medium fairly hot very hot  and  very dim dim medium fairly bright very bright

Are there any stars that seem out of place?. How might you explain them? Get with your group or neighbors and see if you can propose any solutions. How, for example, might a star be very very hot, but not very bright? What other factors might affect the overall brightness?

Relating Position on Diagram to Characteristics of Star

Astronomers reasoned that if a star were hotter, it should have a higher luminosity, and a cooler star would be dimmer. As it turns out, most stars fit this pattern. They can be found on the HR Diagram in the large group that stretches across the middle of the diagram. These are called the Main Sequence

Our sun is a main sequence star, as are many stars close to our solar system in our galaxy.

If you look at it directly, it looks "bright", but could it light up you entire classroom?