?天文学astronomy
?银河系Galaxy;
?太阳系solar system;
?恒星fixed star;
?行星 planet;
?水星Mercury;
?金星Venus;
?地球Earth;
?火星Mars;
?木星Jupiter;
?土星Saturn;
?卫星satellite;
?彗星comet;
?流星meteor;
?轨道orbit;
?公转revolve;
?自传rotate;
?大气层 atmosphere
