The Quran isn't a Textbook. The purpose of the Quran is to guide the spiritual and moral life of the people, not to provide technical documentation on the working of the world. Non-muslims who expect every single sentence of the Quran to be literal and scientifically accurate, even when taken out of context are being unreasonable ... muslims who expect that are misguided and delusional.
Large parts of the Quran are narratives. Like any good narrative and poem (Quran is a Rhyme in original Arabic), language is used to create atmosphere, words are used creatively to have desired effects, vocabulary is used to evoke and maintain a certain tone and rhythm. Common expressions, phrases and idioms are used and convoluted sentences are avoided. It would sound totally absurd if every sentence was literally scientifically accurate.
At 18:86 the Quran is telling us a story of a man named "Dhul-Qarnayn" ( a conqueror, similar to and sometimes disputably linked with Alexander the Great), who once traveled west until sunset, until he saw the sun setting in a body of water:
