1. 外层空间   astronaut   planet   universe   outer space   Hint Half-n-half Clue   2. 彗星   planet   satellite   comet   moon   Half-n-half Clue   3. 月亮   moon   universe   meteorite   light years   Half-n-half Clue   4. 大气   Earth   satellite   atmosphere   planet   Half-n-half Clue   5. 天文学家   moon   universe   astronomer   star   Half-n-half Clue   6. 地球   comet   asteroid   astronaut   Earth   Half-n-half Clue   7. 太阳系   comet   Earth   solar system   gravity   Half-n-half Clue