The celestial equivalent of latitude for the Moon or Sun. When the Moon stands well north or south of the equator, the two tidal bulges are tilted relative to the equator, so a given place passes through one bulge more squarely than the other and the two daily highs differ. The Moon's declination swings from north to south and back every 27.3 days, reaching a monthly maximum between about 18 and 29 degrees depending on the nodal cycle.
Moon's at max declination this week, so expect the big diurnal inequality and one very low low.
Also heard as
- lunar declination
- solar declination
Related terms
Diurnal inequality
How much the day's two high waters, or its two low waters, differ in height from each other.
Tropic tide
A tide occurring when the Moon is near its greatest declination, giving the largest daily inequality.
K1
The lunisolar diurnal constituent, period about 23.93 hours, a main driver of once-daily tides.
O1
The principal lunar diurnal constituent, period about 25.82 hours, created by the Moon's declination.
Nodal cycle
The 18.6-year cycle in the tilt of the Moon's orbit that slowly raises and lowers tidal ranges.