Full moon (this usage has been noted as "erroneous" by "Sky & Telescope" in 1999). According to either definition, "blue moons" occur with the average frequency of intercalary months, seven times in 19 years, the "Farmers' Almanac" system of "full moon names" effectively defining a lunisolar calendar. Full moon The full moon is the lunar phase when the Moon appears fully illuminated from Earth's perspective. This occurs when Earth is located between the Sun and the Moon (more exactly, when the ecliptic longitudes of the Sun and Moon differ by 180°). This means that the lunar hemisphere facing Earth – the near
Equinox Equinox An equinox is commonly regarded as the instant of time when the plane (extended indefinitely in all directions) of Earth's equator passes through the center of the Sun. This occurs twice each year: around 21 March and 22–23 September. In other words, it is the moment at which the center of the visible Sun is directly above the Equator. In the northern hemisphere, the equinox in March is called the Vernal or Spring Equinox; the September equinox is called the Autumnal or Fall Equinox. However, because the Moon (and to a lesser extent the other planets) cause the motion