earth science
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34 Terms
Q: What are stars mostly made of?
A: Hydrogen and helium.
Q: How does a star’s core composition change over time?
A: Hydrogen decreases and helium increases due to fusion.
Q: Does the surface composition of stars change much?
A: It stays mostly constant but can change in later stages as fusion products move outward.
Q: What is the relationship between a star’s mass and its lifespan?
A: The more massive the star, the shorter its lifespan.
Q: How long do small, low-mass stars live?
A: Billions to trillions of years.
Q: How long do massive stars live?
A: Only millions of years.
Q: What is the Sun’s approximate lifespan?
A: About 10 billion years.
Q: What process powers stars?
Nuclear fusion
Q: What happens during fusion in the Sun?
A: Hydrogen nuclei fuse to form helium and release energy.
Q: What are the stages of a low or medium mass star (like the Sun)?
A: Main sequence → Red giant → Planetary nebula → White dwarf.
Q: What are the stages of a massive star?
A: Main sequence → Red supergiant → Supernova → Neutron star or black hole.
Q: In what order do stars fuse elements?
A: Hydrogen → Helium → Carbon → Oxygen → Silicon → Iron.
Q: What happens to fusion time as elements get heavier?
it gets shorter
Q: Why does fusion stop at iron?
A: Because it no longer releases energy.
Q: Where are elements up to iron formed?
inside stars
Q: Where are elements heavier than iron formed?
A: In supernova explosions.
Q: What determines what elements a star can produce?
its mass
Q: What does the H-R diagram plot?
A: Luminosity (brightness) vs temperature (color).
Q: What type of star is the Sun?
A: A yellow G-type star (~5,800 K).
Q: What happens to the Sun as it becomes a red giant?
A: Its temperature decreases, but brightness increases.
Q: How do stars release energy?
A: Through nuclear fusion.
Q: Why can’t chemical reactions explain the Sun’s energy?
A: They couldn’t last billions of years.
Q: What do spectral lines show about stars?
A: Their composition and life stage.
Q: What elements appear in massive stars nearing the end of life?
A: Heavier elements.
Q: What elements appear in main sequence stars?
A: Mostly hydrogen and helium.
Q: Where is energy produced in the Sun?
A: In the core by fusion.
Q: How does energy travel outward?
A: Through the Sun’s layers, then released at the photosphere as sunlight.
Q: What elements did the first stars contain?
A: Only hydrogen and helium.
Q: What does the discovery of stars with only H & He mean?
A: They are very old, formed before heavier elements existed.
Q: What do low-mass stars become?
A: White dwarfs.
Q: What do medium or high-mass stars become?
A: Neutron stars or black holes.
Q: What happens at the end of a star’s life?
A: It loses mass through supernova or planetary nebula events.
Q: Why do stars lose mass over time?
A: Because some matter is converted into energy (E = mc²).
Q: What happens to mass during a supernova?
A: Large amounts are ejected into space.