The phases of the moon (getsurei) and names of the months

The traditional Japanese calendar was a lunisolar calendar, and great attention was paid to the phases of the moon. A lunar month started and ended with the new moon (shingetsu), and a full moon (mochizuki or mangetsu) marked the middle of the month. Special terms were (and still are) used to describe the two half moons, the first appearing on day seven or eight of the month and the second on day 22 or 23: jōgen no tsuki (上弦の月, so called because the appearance of the setting moon was compared to a bow with its drawstring at the top) and kagen no tsuki (下弦の月, the appearance of the setting moon resembling a bow with its drawstring at the bottom).

The following table lists the other names that were used to describe the different phases of moon during the course of the month (hyphens added for clarity):

Term for the moon	Japanese	Approx. day of lunar month Approx. 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, along with the corresponding season and two common name variants. For the problem of how synchronization with the solar year was handled, see the next table.

Month	Japanese	Season	Other names
Mutsuki	睦月	Spring	Hatsutsuki （初月）, Shōgatsu （正月）
Kisaragi	如月		Umemizuki （梅見月）, Yukigezuki （雪消月）
Yayoi	弥生		Hanamizuki （花見月）, Sakurazuki （桜月）
Uzuki	卯月	Summer	Natsuhazuki （夏初月）, Hananokoshizuki （花残月）
Satsuki	皐月		Sakumozuki （さくも月）, Tagusazuki （田草月）
Minazuki	水無月		Kazemachizuki （風待月）, Seminohazuki （蝉葉月）
Fu(mi)zuki	文月	Autumn	Akihazuki （秋初月）, Tanabatazuki （七夕月）
Hazuki	葉月		Katsurazuki （桂月）, Kosomezuki （木染月）
Nagatsuki	長月		Nezamezuki （寝覚月）, Momijizuki （紅葉月）
Kannazuki	神無月	Winter	Shigurezuki （時雨月）, Koharu （小春）
Shimotsuki	霜月		Yukimizuki （雪見月）, Kamigaerizuki （神帰月）
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 signal seasonal events and also to reconcile the differences that arose between the lunar calendar and the solar year. The winter solstice served as the starting point for making these calculations (the winter solstice was by convention assigned to the Eleventh Month). Each month had two points — a setsu （節） and a chū （中） — and each point was assigned a name associated with a particular season. The chū points provided the basis for numbering the sequence of the lunar (calendrical) months, thus establishing the connection between the two systems.

Intercalary months (urūzuki — 閏月) were inserted when the discrepancy between the solar year (the distance between two chū points being about 30.4 days) and the nominally 30-day lunar calendar (in which the moon completes its cycle in about 29.5 days) left a month without a solar chū point, which in classical times happened about once every three years. The extra “empty” month (that is, lacking the chū point necessary for establishing a position in the overall sequence) was given the same number as the previous month, preceded by the term jun （閏）. Thus, jun-nigatsu would be the Intercalary Second Month of the year, following the usual Second Month. The addition of the extra month would bring the two systems back into alignment. Years with the standard 12 lunar months — which themselves could be either 29 or 30 days long — actually contained 354 or 355 days, while years with intercalary months were either 383 or 384 days long. It was a cumbersome system that reached its final iteration in 1844, when the calendar — referred to since the Meiji period as the kyūreki, or “old calendar” — was officially revised in accordance with Japanese methodology for the fourth time in history (the first revision had come in 1685).

The following table gives the names of the 24 solar terms, along with approximate equivalents in the Gregorian system (approximate because the precise date depends upon the year):

Season	Solar term (sekki)	Name	Japanese	Approx. Gregorian equvalent
Spring	shōgatsu-setsu	risshun (beginning of the year)	立春	February 4
	shōgatsu-chū	usui	雨水	February 19
	nigatsu-setsu	keichitsu	啓蟄	March 6
	nigatsu-chū	shunbun (spring equinox)	春分	March 21
	sangatsu-setsu	seimei	清明	April 5
	sangatsu-chū	koku’u	穀雨	April 20
Summer	shigatsu-setsu	rikka (start of summer)	立夏	May 6
	shigatsu-chū	shōman	小満	May 21
	gogatsu-setsu	bōshu	芒種	June 6
	gogatsu-chū	geshi (summer solstice)	夏至	June 21
	rokugatsu-setsu	shōsho	小暑	July 7
	rokugatsu-chū	taisho	大暑	July 23
Autumn	shichigatsu-setsu	risshū (start of autumn)	立秋	August 8
	shichigatsu-chū	shosho	処暑	August 23
	hachigatsu-setsu	hakuro	白露	September 8
	hachigatsu-chū	shūbun (autumn equinox)	秋分	September 23
	kugatsu-setsu	kanro	寒露	October 9
	kugatsu-chū	sōkō	霜降	October 24
Winter	jūgatsu-setsu	rittō (start of winter)	立冬	November 8
	jūgatsu-chū	shōsetsu	小雪	November 23
	jūichigatsu-setsu	taisetsu	大雪	December 7
	jūichigatsu-chū	tōji (winter solstice)	冬至	December 22
	jūnigatsu-setsu	shōkan	小寒	January 6
	jūnigatsu-chū	daikan	大寒	January 21