However, every now and again, a tropical year has 13 full moons, thus one season has four full moons instead of simply three, hence the term "blue moon." This is due to the fact that other full moons with unique names must occur at their proper periods of the year. For example, if we skipped around from July to October, people would be asking why we aren't having any full moons in October.
These special full moons are called "Blue Moons" because they occur when the Moon is also blacked out by Earth's shadow. Only 8% of the sky is dark enough to see such a shadow move across.
The only time when all tropical years have 13 full moons is every 4 years when there are 730 days in a year, but only 604 days between lunar eclipses. At other times, some years will have 12 or 14 full moons, others will have 10 or 6. The reason for this is simple: Lunar months vary depending on where you are on Earth. Near the Equator, the month of Luna is almost exactly 29 days long, while farther away it is slightly longer (or shorter).
All this means that every now and again, you will get a series of consecutive full moons within a year. These events are called "Moonstorms". The next one will be in August 2015.
The additional days add up, and every two or three years (seven times in the Metonic cycle's 19-year cycle), there is an extra full moon in the year. The additional full moon must fall during one of the four seasons, giving that season four full moons rather than the usual three, and hence a "blue" moon. A red moon occurs when there is a total lunar eclipse.
A white moon happens when the earth is between the sun and the moon. Only about half of the sun's rays reach the moon at this time, leaving the remaining half to be reflected back to Earth. This has the effect of making the moon look white or silvery rather than darkish-gray.
A black moon is a term used by farmers when there is a total lunar eclipse and it is night when they should be planting but aren't because of darkness brought on by the eclipse. It is said that if you see a black moon, you will have bad luck for at least part of the month it takes place in.
A red moon is a term used by farmers when there is a total lunar eclipse and it is day when they should be harvesting their crops but aren't because of darkness brought on by the eclipse. It is said that if you see a red moon, you will have good luck for at least part of the month it takes place in.
A green moon is when forests grow back faster than we can cut them down.
It was dubbed the "Blue Moon" since it was the second of two full moons in the same month. There's another way to say "blue moon." It can also be the third of four full moons in a calendar year. A season is the time between the solstices and equinoxes. So, a blue moon occurs when there are four seasons in one year, but only three of them are good ones.
The term "Blue Moon" first appeared in print in 1866 in the diary of Abraham Lincoln. He wrote that there had been a total of five moons this year, including two nights - May 5 and 6 - when they were all together at once. He went on to say that he hadn't seen a more beautiful or unusual moon "since my boy Lincoln was alive."
Lincoln wasn't the only one to call attention to this rare event. Farmers used to mark their crops to see if it would help them predict better when they should plant in order to have a successful harvest. If it was the blue moon, it was believed that plants would not grow unless cultivated at least once during that season.
Today, people use the phrase "once in a blue moon" to describe something that happens very rarely. The word "moon" comes from the name of the lunar goddess. She was known for her cycles and changesability. Sometimes she gave life, sometimes she took it.