The Mid Autumn Festival is celebrated on the day of the full moon close to the astronomical Autumnal Equinox (September 23rd in Gregorian Calendar), which is the day of equal day and night length. The celebration exactly takes place on the 15th day of the 8th lunar month. Roughly the traditional Chinese Calendar is a hybrid between the lunar and the solar calendar. There are 12 lunar months starting at dark moon at 11 pm. To correct the gap to the solar phenomena (which is important for agriculture, for example), every second or third year has an intercalary lunar month, so that the sun always enters Capricorn in month 11.
The Mid Autumn Festival is a harvest festival and related to the Chinese myth on Houyi (后羿) and Chang’e. People celebrate with lanterns and exchange (a lot!) of Mooncakes, which are usually very sweet cakes holding an egg yolk in its inner. Last year, I enjoyed very much going to the Hung Sing Ye Beach which was covered with thousands of lanterns, by the families sitting together in the sand. This year I was unfortunately struggling with some food poisoning and missed, while I dropped in bed early. But at least the full moon was shining bright in my window. This was my last Moon Festival in China.