spring tide: When the sun, moon and earth are aligned.
neap tide: When at right angles the forces are not aligned.
The time between spring and neap is approximately 7 days.
Here's a link to a Coastal Navigation site with a marvelous animated illustration, chart, and full tidal story:
http://www.sailingissues.com/navcourse6.htmlFrom the site:
The earth is also in orbit around the sun (one turn in one year) creating not only another centrifugal force but also a gravitational interaction. These two yield a bulge on the night site (centrifugal) and bulge on the day site (gravitational) both of them moving as the world turns. Therefore, a certain place on this world will experience two high and two low tides each day.
With these forces alone, we would not have
spring tides and
neap tides.
Spring tides have higher high tides and lower low tides whereas
neap tides have lower high tides and higher low tides. Hence, the range (difference in water level between high and low tide) is much larger in a
spring tide than in a low tide.
The Only WO'N!
