Blue Moons and Lunar Leap Months

On the evening of August 31, a blue moon will rise over North America.  No, the moon will not appear blue to the naked eye.  Rather, it will be the 2nd full moon to rise in the month of August.

Usually, only one full moon occurs in every calendar month.  But, about once every 3 years, there will be one month in the year with 2 full moons.  The reason is because it takes the moon about 29 days to go around the Earth.  That is, each full moon occurs about 29 days after the previous one.  But a calendar month is 28-31 days long.  So in most months, the full moon occurs a few days earlier than it did the month before.  And so, about once every three years, there will be a month where a full moon occurs very early in the month, and a second full moon occurs again before the month is over.  This month, the first full moon occurred on August 2, and now a second one is occurring on August 31.

Notably, this particular blue moon is the first to occur since the death of Neil Armstrong, the first human being to walk on the moon.  Neil Armstrong was the commander of the Apollo 11 spacecraft, which landed on the moon on July 20, 1969.  It was Armstrong who said, upon setting foot on the moon for the first time:  "That's one small step for man, one giant leap for mankind".   He died on August 25.


In North America, a blue moon is a slightly unusual astronomical event, and not much more.  But in Asia, it's a much more significant phenomena.

Many Asian countries operate on a lunisolar calendar, that is a calendar that is based in part on the motion of the moon, and in part on the motion of the Earth around the sun.  In North American, the calendar is entirely solar.  In this calendar, the time it takes the Earth to go around the sun (one solar year) is divided into 12 months, which have approximately, but not exactly, the same number of days.  In a lunisolar calendar, a month is defined as the time it takes the moon to go around the Earth.  Thus, each month of the year has exactly the same number of days, that is 29 days.  This is because it takes the moon 29 days to go around the Earth.  During most solar years, there are 12 full moons.  Therefore, there are 12 lunar months in most solar years.  However, in some solar years (essentially the same years in which a blue moon occurs), there are 13 full moons, and therefore 13 months in the year.  In such years, the 13th month is called a "lunar leap month".

The full moon (but not a blue one) rising over the GwangAn bridge.

The Korean calendar is lunisolar.  They use the same calendar as North Americans do for everyday purposes, but the dates of some important holidays are set according to a lunar calendar.  This is why Chuseok (추석), the Korean thanksgiving holiday, and Sollal (설날), the Korean new-year holiday, occur at different dates every year.

In Korean, a leap month is called a yun-dal (윤달).  The last leap month occurred between April 21 and May 20 of this year.  For some Koreans, a leap month is traditionally a period during which the gods are not paying too much attention to the activities of humans.  So, a leap month is the best time to do things that are not likely to be seen in a favourable light by one's ancestors, like digging up their remains and having them cremated.

The idea of cremating a deceased relative after having already buried him / her may appear odd.  However, this happens quite often these days, in Korea, as a result of recent changes in the local burial customs.  Traditionally, Koreans have buried their deceased relatives in simple burial mounds, usually on the many mountains that dot the Korean countryside.  But because the population of Korea has grown so large, mountain burials have recently been outlawed, or at least officially discouraged, for obvious practical reasons.  Furthermore, the government encourages families whose relatives are already buried on mountains to have their remains cremated and relocated.  According to one news article, so many families have chosen to do this during the last leap month that the city of Seoul had to double its offering of cremation services during that period.

A burial mound by a tree, in HaeSinDang park.

A small burial mound in a clearing on GeumJeong mountain, in Busan.

A small Christian graveyard, on GeumJeong mountain, in Busan.