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It is fundamentally a question of spectral lines. Type I supernovae have no hydrogen lines, and type II have strong hydrogen lines. Type 1b have strong helium lines and no hydrogen lines, and type 1c have neither helium nor hydrogen lines. That’s why they aren’t designated as type II supernovae. The reason why type 1b and 1c supernovae have no hydrogen lines ...


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The distinction between gas giants and ice giants is a distinction that works nicely in our solar system. (And don't forget the distinction between the giant planets and the terrestrial planets, which also works nicely in our solar system.) I strongly doubt that these distinctions are universal. Just before the end of the 20th century, astronomers and ...


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