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Observations from what two parts of the electromagnetic spectrum reveal that the Galaxy has spiral arms.
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Q23: The Hubble classification for a spiral galaxy
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Q44: Cepheid stars are useful to astronomers as
Q54: How does the diameter of a black
Q72: Which of the following is a necessary
Q72: The universe has been expanding for billions
Q90: If a star ended its main-sequence life
Q96: What surprising conclusion about the distribution of
Q98: Stars between 0.4 and 4 solar masses