Full moon is called a blue moon. The term "blue moon" used in this sense may date to as early as the 16th century, but it became well known in the United States due to the "Farmers' Almanac" (published since 1818). According to the "Farmers' Almanac", a "blue moon" is the third full moon in any period between either solstice and equinox, or between equinox and solstice, (calculated using the mean tropical year), which contains four full moons. These seasons are equal in length, unlike the astronomical ones, which vary in length depending on the Earth's speed in its elliptical orbit round
Equinox a larger antenna has a narrower beam-width and hence experiences shorter duration "Sun outage" windows.) Equinoxes occur on any planet with a tilted rotational axis. A dramatic example is Saturn, where the equinox places its ring system edge-on facing the Sun. As a result, they are visible only as a thin line when seen from Earth. When seen from above – a view seen during an equinox for the first time from the "Cassini" space probe in 2009 – they receive very little sunshine, indeed more planetshine than light from the Sun. This phenomenon occurs once every 14.7 years on