Beautiful moon in the 13th night 2017/11/2

In Tokyo we could enjoy beautiful and clear moon last night. It was 13th night of 9th month by lunar calendar. It is a traditional prevailing custom in Japan to cerebrate the moon of 13th night of 9th month as lively as the big cerebration of the 15th night of 8th month.

It is popular in the world to enjoy beautiful moon in the 15th night of 8th month by lunar calendar but to enjoy 13th night month is unique custom in Japan.


By lunar calendar one month is composed of 29 days or 30 days. If the moon travels on perfect circle with constant speed, full moon should falls on 14th or 15th night. However the moon travels actually on ellipse circle with unstable speed. Therefore full moon moves from 13th night to 17th night.

With more than 40 % possibility, we can expect full moon in 15th night while it is only little chance to have full moon in 13th night.  People know they can’t expect full moon in that night but they are prepared to enjoy insufficient full moon or unfinished full moon.

It is common tendency for Japanese to prefer unfinished situation rather than perfect or completed situation.


It is time of harvest of agricultural products and various chestnuts. It is also the best season to watch moon shining in the clear autumn sky, with a variety of autumn harvests.

 moon in 13th night