Tropical Month : The average period of the revolution of the Moon around the Earth with respect to the vernal equinox. Its length is approximately 27.321,582 days
National Oceanic and Atmospheric Administration NOAA, Tide and Current Glossary, National Ocean Service, CO-OPS, Products and Services N/OPS3, Silver Spring, MD, USA 1999. http://co-ops.nos.noaa.gov/publications/glossary2. pdf, (ND/ Tide and Current - Amer) {830}