ASTR 1102 final Exam 2025 | Updated Questions
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The Sun has a lifetime of 10 billion years. If a B star has a mass of 10 M◉ and a
luminosity of 10,000 L◉, how long will it live for?
A) 1 billion years
B) 100 million years
C) 10 million years
D) 1 million years ---------CORRECT ANSWER-----------------C
An A5 star has 5x the mass of the Sun, but 15x the luminosity. How long will it
live?
A) 1/3rd of the Sun's lifetime
B) 1/5th of the Sun's lifetime
C) 3 times the Sun's lifetime ---------CORRECT ANSWER-----------------A
Why is the sun gradually and very slowly get's brighter during its lifetime in the
main-sequence?
A) Because newly made helium in the core of the sun produces more nuclear
energy via fusion during the main-sequence.
B) Because as hydrogen converts to helium in the core, the pressure slowly
decreases and gravity slowly compresses the core making it hotter therefore
producing more luminosity.
,C) Because it continues to burn hydrogen in a thin shell around the core. ---------
CORRECT ANSWER-----------------B
Which of the following reaction rates is more sensitive to temperature?
A) The CNO cycle
B) The 3α process
C) The proton-proton (pp) chain ---------CORRECT ANSWER-----------------B
Which of the following reaction pairs burn hydrogen to helium?
A) The CNO cycle and the 3α process
B) The 3α process and the pp chain
C) The proton-proton (pp) chain and the CNO cycle ---------CORRECT ANSWER-------
----------C
How do red giant stars generate energy?
A) Fusion of hydrogen in their core
B) Fusion of hydrogen in a shell around their core
C) Fusion of helium in their core
D) Fusion of helium in a shell around their core
E) Fusion of carbon ---------CORRECT ANSWER-----------------B
Why after the 'helium flash' stars become less luminous in the HR diagram?
,A) Because a hydrogen-burning shell around the core does not produce as much
energy as hydrogen-core burning, therefore luminosity drops.
B) Because they have exhausted their main nuclear fuel and no reactions can
produce more luminosity in the core.
C) Because hydrogen fusion produces less energy and therefore the luminosity
drops.
D) Because the core expands, the temperature drops and therefore the reaction
rates and the luminosity drops so the envelope contracts and heat up. ---------
CORRECT ANSWER-----------------D
A star is 10 times more massive than the sun and 2000 times more luminous. How
many years will it spend in the main-sequence? Reminder: The sun's main-
sequence lifetime is 10 billion years.
A) 50 million years
B) 500 million years
C) 5 million years ---------CORRECT ANSWER-----------------A
Once the star in Part 1 of the Assignment burns the hydrogen in its core and
leaves the main sequence, what type of reaction will be taking place in the core
involving helium?
A) The CNO Cycle
B) The pp-chain
C) The 3α process ---------CORRECT ANSWER-----------------C
, What type of nuclear burning is going on in the sun right now?
A) CNO cycle
B) pp-chain
C) Triple-alpha ---------CORRECT ANSWER-----------------B
What type of nuclear burning will take place in the hydrogen shell of the sun
when it becomes a sub-giant star?
A) CNO cycle
B) pp-chain
C) Triple-alpha ---------CORRECT ANSWER-----------------A
What types of nuclear burning will take place in the hydrogen shell of the sun
when it becomes a giant star?
A) CNO cycle
B) pp-chain
C) Triple-alpha ---------CORRECT ANSWER-----------------A or B
Which type of cluster should have the highest abundance of heavy elements
(metals)?
A) Open cluster
B) Globular cluster ---------CORRECT ANSWER-----------------A
There are many clusters of stars in the galaxy. All the stars in a cluster are usually
the same age. Which type of cluster should appear bluest?
A) Young clusters
B) Middle-aged clusters
and Correct Answers | Already Graded A+ |
verified Answers | Just Released
The Sun has a lifetime of 10 billion years. If a B star has a mass of 10 M◉ and a
luminosity of 10,000 L◉, how long will it live for?
A) 1 billion years
B) 100 million years
C) 10 million years
D) 1 million years ---------CORRECT ANSWER-----------------C
An A5 star has 5x the mass of the Sun, but 15x the luminosity. How long will it
live?
A) 1/3rd of the Sun's lifetime
B) 1/5th of the Sun's lifetime
C) 3 times the Sun's lifetime ---------CORRECT ANSWER-----------------A
Why is the sun gradually and very slowly get's brighter during its lifetime in the
main-sequence?
A) Because newly made helium in the core of the sun produces more nuclear
energy via fusion during the main-sequence.
B) Because as hydrogen converts to helium in the core, the pressure slowly
decreases and gravity slowly compresses the core making it hotter therefore
producing more luminosity.
,C) Because it continues to burn hydrogen in a thin shell around the core. ---------
CORRECT ANSWER-----------------B
Which of the following reaction rates is more sensitive to temperature?
A) The CNO cycle
B) The 3α process
C) The proton-proton (pp) chain ---------CORRECT ANSWER-----------------B
Which of the following reaction pairs burn hydrogen to helium?
A) The CNO cycle and the 3α process
B) The 3α process and the pp chain
C) The proton-proton (pp) chain and the CNO cycle ---------CORRECT ANSWER-------
----------C
How do red giant stars generate energy?
A) Fusion of hydrogen in their core
B) Fusion of hydrogen in a shell around their core
C) Fusion of helium in their core
D) Fusion of helium in a shell around their core
E) Fusion of carbon ---------CORRECT ANSWER-----------------B
Why after the 'helium flash' stars become less luminous in the HR diagram?
,A) Because a hydrogen-burning shell around the core does not produce as much
energy as hydrogen-core burning, therefore luminosity drops.
B) Because they have exhausted their main nuclear fuel and no reactions can
produce more luminosity in the core.
C) Because hydrogen fusion produces less energy and therefore the luminosity
drops.
D) Because the core expands, the temperature drops and therefore the reaction
rates and the luminosity drops so the envelope contracts and heat up. ---------
CORRECT ANSWER-----------------D
A star is 10 times more massive than the sun and 2000 times more luminous. How
many years will it spend in the main-sequence? Reminder: The sun's main-
sequence lifetime is 10 billion years.
A) 50 million years
B) 500 million years
C) 5 million years ---------CORRECT ANSWER-----------------A
Once the star in Part 1 of the Assignment burns the hydrogen in its core and
leaves the main sequence, what type of reaction will be taking place in the core
involving helium?
A) The CNO Cycle
B) The pp-chain
C) The 3α process ---------CORRECT ANSWER-----------------C
, What type of nuclear burning is going on in the sun right now?
A) CNO cycle
B) pp-chain
C) Triple-alpha ---------CORRECT ANSWER-----------------B
What type of nuclear burning will take place in the hydrogen shell of the sun
when it becomes a sub-giant star?
A) CNO cycle
B) pp-chain
C) Triple-alpha ---------CORRECT ANSWER-----------------A
What types of nuclear burning will take place in the hydrogen shell of the sun
when it becomes a giant star?
A) CNO cycle
B) pp-chain
C) Triple-alpha ---------CORRECT ANSWER-----------------A or B
Which type of cluster should have the highest abundance of heavy elements
(metals)?
A) Open cluster
B) Globular cluster ---------CORRECT ANSWER-----------------A
There are many clusters of stars in the galaxy. All the stars in a cluster are usually
the same age. Which type of cluster should appear bluest?
A) Young clusters
B) Middle-aged clusters
