The accurate measurement of time

If a Babylonian who lived four thousand years ago could reappear in the modern world, one of the very few scientific appliances which he could recognize would be the sundial. In use at least as early as 2000 B.C. in Mesopotamia, it has survived in innumerable variations in design to the present day. The limitation of the sundial is, of course, that it serves only on clear days. Watchers of the sky at night must have learned at an equally early age to read the time from the appearance of the night sky.