🌊 Where the tide is, and where it isn't. This globe shows the tidal range of M2, the lunar semidiurnal constituent and the largest contributor to the tide almost everywhere. Not the tide at any particular moment, but how far the sea can move at each point: the difference between high and low water. Where the range is large the surface bulges outward; where the sea barely moves, it stays flat.

At any one place the tide rises and falls twice a day. Seen globally, it does something else: it rotates. This is M2, the lunar semidiurnal constituent, the largest contributor to the tide almost everywhere. One cycle takes 12 h 25 min, which is why high tide arrives about fifty minutes later each day. On a Spilhaus projection, where the ocean appears as the single connected body it is, the structure becomes readable.