 it was called a galaxy by analogy as if it were a stream and a cloud. it is seen in the winter at the beginning of the night / in the direction of the sky. and it is seen in the summer at the beginning of the night in the middle of the sky. that is why it was said the middle of a stream moistens hajar 1 because its being in the middle of the sky is the time for the palm trees to be moistened in hajar. and the galaxy moves at the end of the night so you see it at the end of every night in a place other than its beginning. that is why dhu alrummah said
وسميت مجرة على التشبيه، كأنها مجر، ومسحب. وهى ترى فى الشتاء اول الليل، / فى ناحية السماء. وترى فى الصيف اول الليل فى وسط السماء. ولذلك قيل سطى مجر، ترطب هجر ١ لأن توسطها السماء وقت لارطاب النخل بهجر. وتنتقل المجرة آخر الليل فتراها فى آخر كل ليلة فى غير موضعها من اوله. ولذلك قال ذوالرمة