The largest purely lunar diurnal constituent, with a period of about 25.82 hours. It exists because the Moon spends half its orbit north and half south of the equator, which makes the two daily bulges unequal at most latitudes. Together with K1 it controls the diurnal inequality, and its amplitude swings by close to 20 percent over the 18.6-year nodal cycle.
O1's nodal factor is near its peak in this part of the cycle, so the diurnal ranges are running well above average.
Also heard as
- principal lunar diurnal
Related terms
K1
The lunisolar diurnal constituent, period about 23.93 hours, a main driver of once-daily tides.
Diurnal tide
A tide with a single high water and a single low water in each lunar day.
Diurnal inequality
How much the day's two high waters, or its two low waters, differ in height from each other.
Nodal cycle
The 18.6-year cycle in the tilt of the Moon's orbit that slowly raises and lowers tidal ranges.