tide
most people grow up thinkung that the tids are caused by the moon and indeed that gravitainoaln pull of the moon is a major factor as is the gravitational effect of the sun but there is another major facter which is less oten mentioned an that is the force created by the rotation of the earth itsel.
as the earth oatates on its axis once every 24 hours if the moon stood still then the moon will be overhead and underfoot once in every24 hours giving (in most places) 2 high and 2 low tides a day but as the moon is also obiting in the same direction as the earth revolves it actually takes about 24 hours and 50 minutes for the moon to be in the same place overhead.
so the period from one high tide to the next is about 12 hours 25 minutes.