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The Phases of the Moon (Getsurei) and Names of the Months
The traditional Japanese calendar was primarily a lunar calendar, and great attention was paid to the phases of the moon. A month started and ended with the new moon, and a full moon marked the middle of the month. The moon first revealed itself as a crescent with its two tips pointing more or less upward, giving rise to a comparison with a bow with the drawstring at the top (called jōgen no tsuki). As the moon waxed and waned, the arch of the bow moved upward and the moon became a kagen no tsuki, or "moon with the drawstring at the bottom" (in each case, the shape refers to the appearance of the moon at the time it sets).
The following table lists the names that were used to describe the different phases of moon during the course of the month:
| Term for the Moon | Japanese | Approximate Day of Lunar Month Approximate Time of Moonrise |
| shingetsu / tsugomori | 新月 / つごもり | 30th day of the month 6 a.m. |
| futsuka-zuki | 二日月 | 2nd day of the month 7:30 a.m. |
| mika-zuki | 三日月 | 3rd day of the month 8:30 a.m. |
| nanoka-zuki | 七日月 | 7th day of the month 11:30 a.m. |
| yōka-zuki | 八日月 | 8th day of the month 12:30 p.m. |
| kokonoka-zuki | 九日月 | 9th day of the month 1:30 p.m. |
| tōka-amari no tsuki | 十日余りの月 | 11th day of the month 2:30 p.m. |
| jūsan'ya-zuki / komochi-zuki | 十三夜月 | 13th day of the month 4:30 p.m. |
| mochi-zuki / mangetsu | 望月 / 満月 | 15th day of the month 6:30 p.m. |
| izayoi-zuki | 十六夜月 | 16th day of the month 6:30 p.m. |
| tachimachi-zuki | 立ち待ち月 | 17th day of the month 7 p.m. |
| imachi-zuki | 居待ち月 | 18th day of the month 8 p.m. |
| fushimachi-zuki / nemachi-zuki |
伏し待ち月 / 寝待ち月 | 19th day of the month 9 p.m. (ariake, or lingering moon, from about this point) |
| fukemachi-zuki / hatsuka-zuki |
更け待ち月 / 二十日月 | 20th day of the month 10 p.m. |
| hatsuka-amari no tsuki | 二十日余りの月 | 22nd day of the month 10:30 p.m. |
| nijūsan'ya-zuki | 二十三夜月 | 23rd day of the month 12:30 a.m. |
The Names of the Months
The months, though often simply called the First Month, the Second Month, and so on, also had a variety of other names. The table below gives the most common traditional names for the 12 lunar months of the year, along with two variants and the the seasons that were associated with each month. For the problem of how synchronization with the solar year was handled, see the next tab.
| Season | Month | Japanese | Other Names |
| Spring | 1 - Mutsuki | 睦月 | Hatsutsuki （初月）, Shōgatsu （正月） |
| 2 - Kisaragi | 如月 | Umemizuki （梅見月）, Yukigezuki （雪消月） | |
| 3 - Yayoi | 弥生 | Hanamizuki （花見月）, Sakurazuki （桜月） | |
| Summer | 4 - Uzuki | 卯月 | Natsuhazuki （夏初月）, Hananokoshizuki （花残月） |
| 5 - Satsuki | 皐月 | Sakumozuki （さくも月）, Tagusaziki （田草月） | |
| 6 - Minazuki | 水無月 | Kazemachizuki （風待月）, Seminohazuki （蝉葉月） | |
| Autumn | 7 - Fuzuki | 文月 | Akihazuki （秋初月）, Tanabatazuki （七夕月） |
| 8 - Hazuki | 葉月 | Katsurazuki （桂月）, Kosomezuki （木染月） | |
| 9 - Nagatsuki | 長月 | Nezamezuki （寝覚月）, Momijizuki （紅葉月） | |
| Winter | 10 - Kannazuki | 神無月 | Shigurezuki （時雨月）, Koharu （小春） |
| 11 - Shimotsuki | 霜月 | Yukimizuki （雪見月）, Kamigaerizuki （神帰月） | |
| 12 - Shiwasu | 師走 | Umehatsuzuki （梅初月）, Harumachizuki （春待月） |
The 24 Solar Terms - Nijūshi Sekki
Solar terms (sekki -- 節気), which mark points 15 degrees apart along the solar elliptic, were used to adjust the differences that arose between the lunar calendar and the solar year. The winter solstice served as the starting point for these calculations. Each month had two points -- a setsu （節）and a chū （中）-- and each point was given a name that identified a particular season, with the chū point serving as the basis for giving the month its name. Intercalary months (urūzuki -- 閏月) were inserted when the discrepancy between the lunar calendar and the solar year (as reckoned by the sekki system) left a lunar month without a chū point, which happened about once every three years. The "empty" month (empty because the period between new moons did not contain a chū point, leaving the month nameless) was given the same name as the preceding month, preceded by the term jun （閏）. Thus, jun-nigatsu would be the Intercalary Second Month of the year, following the usual Second Month. Lunar years normally contained about 354 days, while years with intercalary months were about 384 days long. It was an extraordinarily complex system.
The following table gives the names of the 24 solar terms, along with their approximate equivalents in the Gregorian system:
| Season | Solar Term |
Name (English) | Name (Japanese) | Approximate Solar Equivalent |
| Spring | shōgatsu-setsu | risshun | 立春 | February 4 (beginning of the year) |
| shōgatsu-chū | usui | 雨水 | February 19 | |
| nigatsu-setsu | keichitsu | 啓蟄 | March 6 | |
| nigatsu-chū | shunbun | 春分 | March 21 (spring equinox) | |
| sangatsu-setsu | seimei | 清明 | April 5 | |
| sangatsu-chū | kokuu | 穀雨 | April 20 | |
| Summer | shigatsu-setsu | rikka | 立夏 | May 6 (start of summer) |
| shigatsu-chū | shōman | 小満 | May 21 | |
| gogatsu-setsu | bōshu | 芒種 | June 6 | |
| gogatsu-chū | geshi | 夏至 | June 21 (summer solstice) | |
| rokugatsu-setsu | shōsho | 小暑 | July 7 | |
| rokugatsu-chū | taisho | 大暑 | July 23 | |
| Autumn | shichigatsu-setsu | risshū | 立秋 | August 8 (start of autumn) |
| shichigatsu-chū | shosho | 処暑 | August 23 | |
| hachigatsu-setsu | hakuro | 白露 | September 8 | |
| hachigatsu-chū | shūbun | 秋分 | September 23 (autumn equinox) | |
| kugatsu-setsu | kanro | 寒露 | October 9 | |
| kugatsu-chū | sōkō | 霜降 | October 24 | |
| Winter | jūgatsu-setsu | rittō | 立冬 | November 8 (start of winter) |
| jūgatsu-chū | shōsetsu | 小雪 | November 23 | |
| jūichigatsu-setsu | taisetsu | 大雪 | December 7 | |
| jūichigatsu-chū | tōji | 冬至 | December 22 (winter solstice) | |
| jūnigatsu-setsu | shōkan | 小寒 | January 6 | |
| jūnigatsu-chū | daikan | 大寒 | January 21 |
Times and Directions
In addition to their role as signs of the zodiac, the Twelve Branches were also used to refer to times of the day and geographical directions. The following graphs illustrate the relationships.
Times
The day was divided into halves, with the two-hour period centered
on midnight designated as the Hour of the Rat. When finer
distinctions were necessary, these two-hour periods were
further divided into quarters. Another way of calculating
time seems to have been based on the importance to divination
of multiples of nine, so that the first instance (corresponding
to midnight) is kokonotsudoki ("nine of the
clock"), and a countdown of sorts begins there, with
two times nine equal to 18, which, when the leading digit
is ignored, yields yatsudoki ("eight of the
clock"), three times nine equals 27, and hence 27 --> 7--> nanatsudoki ("seven
of the clock"), and so on, down to yotsudoki ("four
of the clock"). There were variations on this system
in different historical periods, other terms exist for different
ranges of time within the 24-hour day, and in addition there
is a theory that holds that the Hour of the Rat actually
began at midnight, so that the method indicated by the graph
cannot be considered perfectly reliable in all cases.
Directions
Each of 12 directions took the name of one of the Branches,
beginning with the Rat in the north, with the northeast,
southeast, southwest, and northeast given special designations
based on the names of the adjoining Branches. The northeast
and southwest were considered unlucky directions (kimon and urakimon,
respectively), forming the basis for the practice of avoiding
them (katatagae).
