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formation × 40star × 5
the-moon × 5
galaxy × 5
planetary-formation × 5
solar-system × 4
universe × 4
natural-satellites × 4
planet × 3
planetary-ring × 3
early-universe × 3
the-sun × 2
asteroids × 2
milky-way × 2
atmosphere × 2
big-bang-theory × 2
comets × 2
mass × 2
star-formation × 2
saturn × 2
hydrogen × 2
black-hole × 1
orbit × 1
observational-astronomy × 1
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