Chapter 11 Quiz: Olivia Ward

1. How do we measure stellar luminosities?
   
   The luminosity of a star, the amount of power it radiates, can be determined by the following equation:
   Luminosity = 4π (distance)^2
2. How do we measure stellar temperatures?
   
   The lines in a star's spectrum correspond to a sequence of spectral types, which determine the star's temperature: OBAFGKM, going from hottest to coolest.
   
   
3. How do we measure stellar masses?
   
   Stellar masses are measured by the binary star system using Newton's version of Kepler's third law. We need the measurements of their orbital period and the separation between the two.
   
   
4. What is a Hertzsprung-Russel diagram?
   
   An H-R diagram plots stars according to their surface temperatures and luminosities. This diagram shows the narrow band called the main sequence. Giants and super giants are in the upper right, and white dwarfs are in the lower left of the main sequence.
5. What is the significance of the main sequence?
   
   The stars on the main sequence are fusing H into He in their cores. The star's position in the main sequence depends on its mass. Stars with high masses are located in the upper left of the main sequence, and the masses get smaller toward the lower right end. The lifetimes of stars are oppositely displayed because high-mass stars live shorter lives.
   
   
6. What are giants, supergiants, and white dwarfs?
   
   Giants and super giants are stars that have exhausted their core supply of H for fusion and are undergoing other forms of fusion because they are at the end of their lives. White dwarfs are the exposed cores of stars that have already died.
   
   
7. What are the two types of star clusters?
   
   The two types of star clusters are open clusters, which contain up to several thousand loosely packed stars, and globular clusters, which contain hundreds of thousands of stars, all closely packed together.
8. How do we measure the age of a star cluster?
   
   The cluster's stars were all born at the same time, so we can find a cluster's age by finding the main-sequence turnoff point of its stars on the H-R diagram. The cluster's age is equal to the core hydrogen fusion lifetime of the hottest and most luminous stars that remain on the main sequence. Open clusters are much younger than globular clusters.
9. Do we know any cluster older than fourteen billion years?
   
   No, we do not, because they would be older than the Universe.
   
   
10. How old is the Universe?
    
    The Universe is 13.77 billion years old.