1. 宇宙   astronomer   outer space   universe   Sun   Hint Half-n-half Clue   2. 轨道   solar system   asteroid   orbit   light years   Half-n-half Clue   3. 光年   gravity   light years   universe   Sun   Half-n-half Clue   4. 星   light years   star   comet   Sun   Half-n-half Clue   5. 宇航员   astronaut   light years   atmosphere   asteroid   Half-n-half Clue   6. 地球   orbit   Earth   planet   star   Half-n-half Clue   7. 大气   atmosphere   solar system   meteorite   moon   Half-n-half Clue