The practical unit for pressure in the ocean, equal to 10 centibars, and is the approximate pressure produced by each meter of overlying water declination: Angular distance north or south of the celestial equator, taken as positive when north of the equator and negative when south. The Sun passes through its declinational cycle once a year, reaching its maximum north declination of approximately 23-1/2^o about June 21 and its maximum south declination of approximately 23-1/2^o about December 21. The Moon has an average declinational cycle of 27-1/2 days which is called a tropical month. Tides or tidal currents occurring near the times of maximum north or south declination of the Moon are called tropic tides or tropic currents, and those occurring when the Moon is over the Equator are called equatorial tides or equatorial currents. The maximum declination reached by the Moon in successive months depends upon the longitude of the Moon's node, and varies from 28-1/2^o when the longitude of the ascending node is 0^o, to 18-1/2^o when the longitude of the node is 180^o . The node cycle, or time required for the node to complete a circuit of 360^o of longitude, is approximately 18.6 years. See: Epoch (2)