As a star exhausts the hydrogen in its core, what happens?
It becomes hotter and more luminous
It becomes hotter and less luminous
It becomes cooler and less luminous
It becomes cooler and more luminous
When does a star experience helium fusion?
just before it enters the main sequence
after it has become a red giant star
when it is on the horizontal branch
before it leaves the main sequence
Why are giant and supergiant stars rare?
The giant and supergiant stages are very short
The star blows up before the giant or supergiant stage is reached
They do not form as often as main sequence stars
The giant or supergiant stage is very long
Which of the following statements best describes why stars eventually die?
Their lifespan is limited
They exhaust all their fuel
Their cores become hotter
They become less luminous
Which of the following occurs during the giant stage?
helium fusion in the core and hydrogen fusion in the surrounding shell
hydrogen fusion in the core and helium fusion in the surrounding shell
hydrogen and helium fusion in the core
In what way are giants and supergiants similar?
They are the main sequence stars
They undergo a helium flash stage as they enter the main sequence
They are very luminous
Their cores expand rapidly to reach giant sizes
What is the term for a collection of 105 to 106 old stars in a region 30 to 100 light-years in diameter?
What is the defining characteristic of stars within a cluster that are at the turnoff point?
They are just leaving the main sequence
They are just becoming white dwarfs
They are just entering the main sequence
They are about to explode in supernovae
What is the approximate age of the star cluster in the H-R diagram? (Hint: Main sequence stars of spectral types O and B have a core supply of hydrogen that is sufficient to last about 250 million years; types A and F, about 2 billion years; type G about 10 billion years; types K and M about 30 billion years. The apparent magnitude scale means that larger numbers are toward the bottom of the vertical axis.)