Moon & the tides

Two bulges, one moon

The moon's gravity pulls the ocean into a bulge on the side facing it — and a matching bulge on the far side, where the earth is pulled away from the water. The earth spins through both each day, so most coasts get two tides.

lunar day   24 hours 50 minutes
tides/day   two, on most coasts
delay       ~50 minutes later each day

That fifty minutes matters

Because the moon rises about 50 minutes later every day, the tide does too. A high tide that's at six today is at 6:50 tomorrow. Plans shift by a little under an hour daily.

The sun's quiet pull

The sun is 27 million times heavier but 390 times farther away. Its tide is small — yet at new and full moon it aligns with the moon's and gives us the spring range.