Winter solstice one must be able to observe a change in azimuth or elevation less than or equal to about 1/60 of the angular diameter of the sun. Observing that it occurred within a two-day period is easier, requiring an observation precision of only about 1/16 of the angular diameter of the sun. Thus, many observations are of the day of the solstice rather than the instant. This is often done by observing the sunrise and sunset or using an astronomically aligned instrument that allows a ray of light to be cast on a certain point around that time. Length of day
Chinese calendar the winter solstice, in a solar year. The 11 mid-climates, except for the winter solstice, are in the 11 or 12 complete months. The complete months are numbered from 0 to 10, and the incomplete months are considered the 11th month. The first month without a mid-climate is the leap, or intercalary, month. Leap months are numbered with "rùn" , the character for "intercalary", plus the name of the month they follow. In 2017, the intercalary month after month six was called "Rùn Liùyuè", or "intercalary sixth month" () and written as "6i" or "6+". The next intercalary month (in