Exam-style question
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Which spectral class would you expect to find on the upper left of a Hertzsprung–Russell diagram?.
- A.O
- B.M
- C.K
- D.G
Model answer
What a good answer should say
- O
Explanation
Why this works
Define both: The upper left of an HR diagram represents high luminosity and high temperature; spectral class O stars occupy this region. Identify key difference: O stars are both luminous and hot, placing them in the upper left, whereas M, K and G stars are cooler and lie lower.
Explain when each applies: Upper left corresponds to hot, massive stars; lower right to cool, low‑mass stars. Conclude: O stars are found in the upper left.
Common mistake
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