This task is about writing a correct answer for the reading comprehension task. Based on the information provided in a given passage, you should identify the shortest continuous text span from the passage that serves as an answer to the given question. Avoid answers that are incorrect or provides incomplete justification for the question.
Q: Passage: The official English name of the system is BeiDou Navigation Satellite System. It is named after the Big Dipper constellation, which is known in Chinese as Beidou. The name literally means "Northern Dipper", the name given by ancient Chinese astronomers to the seven brightest stars of the Ursa Major constellation. Historically, this set of stars was used in navigation to locate the North Star Polaris. As such, the name BeiDou also serves as a metaphor for the purpose of the satellite navigation system. Question: What was the Beidou constellation used for?
A:
to locate the North Star Polaris