From Early Greek Science: Thales to Aristotle:

First, Glaucon assumes that astronomy has been recommended because it is useful.
    Skill in perceiving the seasons, months and years is useful not only to agriculture and         navigation, but also just as much to the military art (527d).
But to this Socrates remarks:
    I am amused that you seem to be afraid lest the many suppose you to be recommending useless studies. (p.67)