9 
Astronomic Fundamental Principles 
2 Astronomic Fundamental Principles 
The chronological sequence of marine tides has been associated with the 
Moon’s and the Sun’s relative positions to Earth already since ancient times. 
A characteristic of North Sea tides is the fact that to each upper culmination of 
the Moon can be assigned a high water and the ensuing low water. On average 
12 h 25 min later, after the lower culmination, follows another high water and 
subsequent low water. The average time passing between the Moon’s transit 
over the prime meridian in upper culmination (or over 180° W in lower culmina 
tion) and the onset of the next following high water is called mean high water 
interval (MHWI). In the German Bight, intervals between 9 h 45 min (Borkum) 
and 16 h 27 min (Geesthacht) are observed; in Cuxhaven, the interval is 11 h 
50 min (cf. Table 3). 
In contrast to wide parts of the global ocean with its fringing and marginal seas, 
the North Sea tides are very regular, in particular within the German Bight; 
mostly these are semi-diurnal with tidal ranges of 2 to 4 m. The astronomically 
explicable deviations of high and low water intervals from their mean values are 
less than 1 h. The correspondent height deviations vary in the amount of less 
than 0,5 m. Because this is so, temporal mean values of levels and intervals 
already provide good approximations for each individual case. 
A detailed illustration of the celestial rudiments of tidal theory shall be dis 
pensed with here. Commendable illustrations of tides as a function of time have 
been published already by Horn (1948 and 1960).