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Why is it surprising that spiral arms are stable structures, lasting billions of years?
Q1: All stars produce an absorption spectra.
Q11: Calculations of the Sun's future evolution indicate
Q20: A supergiant star's radii may extend out
Q23: Matter falling into a black hole arranges
Q29: The central bulge and the galactic disk
Q34: At the longest look-back times, we see
Q54: Which event would you expect to be
Q62: During the first reaction of the proton-proton
Q64: Explain the difference between apparent visual brightness
Q68: Explain the Babcock model and why the