Most people should have heard of the term "double spring and leap month" and said it's a sign of good fortune and great for loved ones to get married. But what exactly is that?

The spring in "double spring" means two "Spring Commences" (SC) in the 24 Solar Terms. Then why are there two SC in a Chinese year? You need to know the basis behind it.

Many people think that the Chinese calendar is one based on the movement of the Moon but this is only half correct. The Chinese calendar uses the movement of the Moon around the Earth to determine the length of a month, but it also makes reference to the position of the Earth relative to the Sun to mark the year. The moon takes about 29.5 days to revolve around the Earth, so the lunar month is sometimes 29 days, sometimes 30 days. From that, a year is about 354 days. But we all know a year is about 365 days and the Earth returns to its original position. There is a difference of 11 days between the lunar and solar year and about a month over 3 years. To account for the difference, on average we add a leap month in 7 years over a period of 19 years and it makes the Chinese calendar about the same as the Gregorian calendar.

Let's return to the saying "Double Spring and Leap Month". As the 24 Solar Terms are determined by the position of the Earth around the Sun, the dates of the Solar Term across different Gregorian years are about the same. When there is a leap month, that year is 385 days long and naturally covers two SC and thus the "double spring" and leap month always occur together.