Article by Clive Goodhead
Tides vary from day to day both in their timing and in height. The tide pages on this Marazion Guide website explain briefly Marazion's and St Michael's Mount's tides and the tide predictions used on this website.
The tides at a particular location are the result of the gravitational influences between the Earth, the Moon and the Sun coupled with the effects of Earth rotation and the depths of local oceans, seas and estuaries.
The orbital details of the Earth, Moon and Sun and the relationships between them are known with a high degree of accuracy. In addition to orbital information, tide prediction requires information (known as tidal constants) derived from an analysis of tides over a long period of time. The tidal predictions on this web site are based on information derived from sea level data obtained from the British Oceanographic Data Centre based at the Proudman Oceanographic Laboratory, Liverpool.
A computer programme using the orbital information and tidal constants information referred to above calculates the predictions of future tides used on this website.
Although, tides can be predicted for any date as far ahead into the future as required, such predictions take no account of the effects of future global sea level rises and changes in seabed topography, which for predictions many decades ahead may be significant.
As well as times, tidal heights vary from day to day as the relative positions of the Earth, Moon and Sun change.
Spring tides occur shortly after New Moon and Full Moon, when the gravitational forces of the Sun and Moon reinforce each other, resulting in a higher than normal tidal range. Spring tides are nothing to do with the season; the name may have been derived from a medieval word meaning to "leap up".
The largest spring tides at Marazion have a tidal range of a little over five metres and occur shortly after the New Moon and Full Moon closest to the equinoxes; these tides are sometimes referred to as "Equinoctial Spring Tides". The spring (or vernal) equinox occurs around 20/21 March, and the autumn equinox occurs around 22/23 September.
Marazion Guide | Guide to Marazion and St Michael's Mount, near Penzance, Cornwall