4.  The H-R Diagram is actually a graph that illustrates the relationship that exists between the average surface temperature of stars and their absolute magnitude, which is how bright they would appear to be if they were all the same distance away.

5.  Rather than speak for the brightness of stars, the term “luminosity” is often used. Luminosity is a measure of how much energy leaves a star in a certain period of time. Generally, for stars that are at equal distances from the Earth, the more luminous a star, the brighter it is.

6.  The luminosity of stars is not only affected by temperature but also by size. The most luminous stars would be those that are large and hot. Those that are least luminous would be small and cool. The color of a star is determined by its surface temperature, which is illustrated on the H-R Diagram.

7. Back page!  Using the H-R Diagram provided with this activity, answer the following questions.

8.  What is the variable on the x axis?

9.  What is the variable on the y axis?

10.  What is the approximate surface temperature of the sun?

11.  Would the surface temperature of the stars classified as white dwarfs be generally higher or lower than that of stars classified as super giants?

12.  What is the color of the stars shown on the diagram that have the highest surface temperature?

13.  What is the color of the stars shown on the diagram that have the lowest surface temperature?

14.  List the colors of the stars from the color of the hottest star to the color of the coldest star.

15.  How many groups of stars are located on the H-R Diagram? White dwarfs, main sequence, super giants, and giants.

16.  Most of the stars shown on the diagram are classified as which type of star? White dwarfs, main sequence, super giants, or giants?

17.  Our sun is classified as which type of star?

18.  Name a star that is very dim and red in color.

19.  Where are the brightest stars found on this diagram?

20.  Where are the dimmest stars found on this diagram?

21.  Where are the coolest stars found on this diagram?

22.  Where are the hottest stars found on this diagram?

23.  Where will we find the hottest and brightest stars?

24.  Where will we find the coolest and brightest stars?

25.  Where will we find the coolest and dimmest stars?

26.  Compare and contrast our sun to Sirius in terms of luminosity, color, and surface temperature. SunSirius Luminosity Color Surface Temperature