Astronomy Stars and Stellar Evolution 2 — Questions and Answers
Question 1: What is the primary source of energy in a main-sequence star like the Sun?
- Nuclear fusion of hydrogen into helium (Correct answer)
- Gravitational collapse
- Chemical combustion
- Nuclear fission of uranium
Correct answer: Nuclear fusion of hydrogen into helium
Main-sequence stars fuse hydrogen into helium in their cores, releasing enormous energy.
Question 2: Which property of a star determines its position on the main sequence?
- Its mass (Correct answer)
- Its distance from Earth
- Its apparent brightness
- Its age only
Correct answer: Its mass
A star's mass sets its temperature and luminosity, fixing its position on the main sequence.
Question 3: What color are the hottest stars?
- Blue (Correct answer)
- Red
- Yellow
- Orange
Correct answer: Blue
Blue stars have the highest surface temperatures, often exceeding 25,000 K.
Question 4: The Hertzsprung-Russell diagram plots luminosity against which stellar property?
- Surface temperature (Correct answer)
- Distance
- Rotation speed
- Magnetic field strength
Correct answer: Surface temperature
The H-R diagram plots luminosity versus surface temperature (or spectral class).
Question 5: What happens to a Sun-like star when it exhausts hydrogen in its core?
- It expands into a red giant (Correct answer)
- It immediately becomes a black hole
- It stays unchanged forever
- It splits into two stars
Correct answer: It expands into a red giant
Core hydrogen exhaustion causes the outer layers to expand and cool into a red giant.
Question 6: What is a protostar?
- A forming star not yet fusing hydrogen steadily (Correct answer)
- A dead remnant of a supernova
- A fully evolved white dwarf
- A planet larger than Jupiter
Correct answer: A forming star not yet fusing hydrogen steadily
A protostar is an early collapsing gas cloud that hasn't yet begun stable core fusion.
Question 7: Which spectral class is used to describe the Sun?
- G (Correct answer)
- O
- M
- B
Correct answer: G
The Sun is a G-type (G2V) star with a surface temperature near 5,800 K.
Astronomy Stars and Stellar Evolution 2
What is the primary source of energy in a main-sequence star like the Sun?