?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
