This is a hybird calendar showing Gregorian year 2020 and the associated Chinese lunisolar year, which was the 37th year of the current 60-year cycle. The Chinese year began on Jan. 25, 2020, and because it was a leap year of 384 days, didn't end until Feb. 11, 2021. Leap years have an entire extra month; in this case, the fourth month happened twice.
If you are familiar with the Hebrew lunisolar calendar, you will find this one to be remarkably similar in many respects. Though they evolved independently, both were developed to meet the same need, and did so in the much the same manner. In both traditions, a new month begins with the dark Moon (also called the new Moon). However, in a purely lunar calendar (of which the Islamic calendar is a prominent example), the months drift freely with respect to the solar year, and will move through all of the seasons over the course of a few decades. As the name implies, a lunisolar calendar melds the lunar calendar with one based on the solar year, which is the time it takes the Earth to complete one orbit of the sun (the Gregorian calendar we use every day is the best-known example of a solar calendar). Most people were farmers, and a lunisolar arrangement met their need for a calendar that remained generally aligned with the seasons from one year to the next.
Below you can find an in-depth description of the various components of the calendar, and explanations for why each has been included and how it relates to the others.
Note that the explanatory information below is only in English, but the calendar itself shows both English and Chinese wherever pertinent, as well as hànyǔ pīnyīn, a system for rendering the pronunciation of Standard Mandarin Chinese using the Latin alphabet with special diacritical marks to represent Chinese Mandarin's four tones .
Chronological motion is anti-clockwise, and starts and ends at the top of the print. The section at the bottom of the print shows every year of the current 60-year cycle, and is described in more depth in the caption of an image appearing below. Because almost all of the cyclical groupings appearing on the calendar number twelve (or a mutiple of twelve), there is a twelve-color code that appears all over the calendar, using colors that are essentially the same as those used in my 2016 calendar.
Here is a what each ring in the main figure represents, starting from the sun at the center and moving outwards:
A. The earth's annual revolution around the sun, showing how the earth's obliquity (also known as axial tilt) of about 23º is responsible for the seasons. The earth is shown on both Equinoxes and both Solstices, so once for each quarter of its orbit.
B. The months of the Chinese lunisolar calendar, which number 13 because it is a leap year. The months are numbered 1 through 4, then a second 4th month occurs, then what are actually the sixth through 13th months are numbered 5 through 12. This ring is effectively repeated as part of ring H, where it is joined by the individual days of the Chinese months.
C and D. Ordinal days of the Chinese lunisolar year. Ring D is an ascending count of days, from 001 to 384, while C is the opposite and represents the number of days remaining in the year. Each day is represented by a tick between the two rings and radial lines moving outward from them, but only days that are multiples of five are written.
E. Weeks of the Chinese lunisolar year. Because it is a leap year, there are almost 55 weeks. Note the alternating bands of lighter and darker background color that show the change of weeks, and continue all the way to the outermost rings; these makes it much easier to move from ring to ring without getting lost. The number of days in a week is within the subitizing range, and weeks are the only grouping of more than one day in common use that is always the same length.
F. Gregorian calendar (GC) months, days of the month, and days of the week.
G through K all pertain to the solar year, rather than the lunisolar year. Where the lunisolar year is driven by the phases of the moon, with each month always beginning at the dark moon, the solar year ignores the moon and is fixed to the earth's movement around sun (actually, the sun's apparent movement across the ecliptic plane; at the time the calendar was developing, it was assumed that it was the sun moving around a fixed earth.)
G. The Chinese seasons. They are translated to be the same four seasons as in the west, but shifted a month and a half earlier, because the Chinese consider the Equinoxes and Solstices to the the precise midpoint of each season rather than its start. Spring, for example, starts Feb. 4 and ends May 4 of the GC, and the Equinox Mar. 20 is its middle.
H shows the 12 "solar terms," which are pairs of the 24 "climate terms" in ring I.
I. There is one climate term every 15º of motion along the ecliptic (24 x 15º = 360º or one full revolution).
J shows the degrees from the 0º point on the Spring Equinox.
K. An arrow emanates from the starting point of each climate term and points to the Chinese lunisolar months in ring
L. This is difficult to represent visually, but this is the connection between the solar year and the lunar months, and that connection enables the lunisolar system. Most months, indeed all the months in most years, will contain two climate terms. When a month only contains a single term, as is the case for the fifth month of this year, that is a leap month, and the year that contains it is a leap year. (To highlight its special status, the lone climate term marker for the leap month is colored differently and is square rather than round for the pairs of markers in the other months.) The month in question is the one treated as the extra month, i.e. as a repeat of its preceding month, which in this case is the fourth month. Following this system allows adherence to the traditional lunar months, while keeping the overall calendar from drifting too far out of alignment with the seasons, which would undermine its usefulness for agricultural purposes.
M. The lunisolar months, days of the month, and days of the week. The first portion of that is a repetition of ring B.
N is a model of the Earth-Moon system showing their positions (distances not to scale) relative to each other and to the sun every 14.75 days, on the dark moon and the full moon. This visualization should make be easy to understand why the Moon's phases happen, if you didn't already know. It takes the Moon approximately 29.5 days to make one orbit of the Earth, or go from one or "new" moon to the next. Chinese lunisolar months therefore alternate in length between being 29 and 30 days long. The same month from year to year will be a different length following a leap year, but the same otherwise (because of the odd vs. even number of intervening months). Incidentally, the reason we always see the same hemisphere (called the "near side" of the Moon—the side we never see is the "far side," sometimes inaccurately called the "dark side"), is that the Moon also takes the same 29.5 days to rotate as it does to revolve. This is not a crazy coincidence, but actually an artifact of the two bodies' gravitational pull on each other, and is known as tidal locking.
O. The outermost ring simply shows the number of every fifth ordinal days of the year, the same as ring D.
The central figure shows the direction the Earth orbits the sun and the direction in which the Earth rotates daily on its axis. Since the perspective here is viewing Earth from above the north pole, the direction of motion is counter-clockwise (as it's called in the US; elsewhere known as anti-clockwise or widdershins). If viewed from above the south pole, as I designed a similar calendar for 2016, the motion would appear clockwise. Neither is more valid than the other, because there is no up or down in outer space, but it turns out that the Chinese solar terms that are published widely without qualification are only applicable north of the equator (which happens to be where the large majority of the members of the Sinosphere resides)! The Earth is shown four times, one for each solstice and each equinox. If you look at the shadows on each globe and imagine it it spinning once a day on its axis, you should be able to see why the equinoxes have the same amount of light and darkness; why the solstices are the longest and shortest days of the year; why, north of the Arctic circle, that means a full 24 hours of darkness at the December solstice and 24 hours of light at the the June solstice; and why all of that is reversed in the Southern Hemisphere.
The Chinese calendar is lunisolar, which means it combines the lunar calendar, in which each month begins on the dark moon (or new moon), with a solar calendar that is fixed to the solar year, the time it takes the Earth to make one revolution around the sun. Since the moon actually takes 29.5 days to complete an orbit, the months alternate between having 29 and 30 days. The solar year, on the other hand, has nothing to do with the moon's phases. It is divided into 24 "climate terms," with each one corresponding to 15 degrees apparent motion across the ecliptic plane. Most lunar months contain two starts of a climate term; when a month has only one, it is a repeat of the previous month, giving its year 13 months. These are called leap years and have 383 or 384 days. Common years have 354 or 355 days. In 2020, the fifth Chinese month had only one term, and so was treated as the second fourth month. The month after, actually the year's sixth month, was considered its fifth, and so on to the end of the year. In 2021, there were no months with only a single term, so no months repeated.
In the Chinese lunisolar calendar, the years are tracked according to their place within a sixty-year (sexagenary) cycle. For longer-term year-keeping, there is no consensus epoch. Traditionally, counting would start over with the beginning of a new monarch's reign. The sexagenary cycle results from the combination of the twelve "earthly branches," each one associated with one of the twelve animals in the Chinese zodiac, with the five "heavenly stems." each associated with one of the traditional Chinese "elements" (wood, fire, earth, metal and water). For each element, there is a stem for yang years and one for yin years, so 12 x (5 x 2) = 60. After the sixtieth year, the cycle begins again. The current cycle began with the year that started on Feb. 2, 1984 of the Gregorian calendar (a wood rat year and leap year), and will end with year that begins on Feb. 10, 2043 (water pig, common year).
