If kids live near the ocean or inlets, the daily fluctuation of tides will be a familiar feature of their lives. What causes them? Correlating tidal cycles (50 minutes later each day) with the lunar cycle shows that tides are caused by the moon–its gravitational pull on the earth. It is easy to visualize how this causes a high tide on the side toward the moon; the high tide on the opposite side is not so easy and has undergone development in understanding. The following video gives the most current understanding, which, note, differs from that in the text. Post questions.