Question 9. Look at the diagram above. What energy level would you expect most of the electrons in atoms of a very hot star to be in?

What energy level would you expect the electrons in atoms of the coolest stars to be in?

Question 10. Look back at your classifications using temperature. What class of star (O,B,A,F,G,K, or M) do you think is most likely to be completely ionized near its surface?

Which type of star do you think is most likely to have molecules in its atmosphere?

Question 11. Recall which atomic transition causes the H-alpha line. Why do extremely hot stars show very little H-alpha absorption?

Why do extremely cool stars show very little H-alpha absorption?

Question 12. Which class of star (in the letter system) is at the ideal temperature for hydrogen to absorb H-alpha photons?

Is this the hottest star?

Is this the coolest star?

Question 13. Stars are composed primarily of hydrogen. But among the stars you classified, stars 1, 4, and 5 have other spectral lines that are much more prominent. If hydrogen is the main component of stars, why isn't Hα the most prominent absorption line in every star?

Question 14. The accepted ordering for spectral classes among astronomers is OBAFGKM. You may have learned the classes with the phrase "Oh, be a fine girl/guy, kiss me." Why do the classes appear in this order?

Why do you think astronomers decided to re-order the spectral classes instead of just redefining what the letters meant (that is, changing what a class "A" star was)?