Why are there such things as leap in May and leap in July?

The saying of leap month comes from the lunar calendar, that is, the lunar calendar or the summer calendar.

It is based on the fact that the moon revolves around the earth for one month and the number of hours that the earth revolves around the sun for one year is actually equal to the lunar calendar.

The lunar calendar is a traditional calendar in China, with an average of 12 months a year, 30 days for the big month, 29 days for the small month, and 354 or 355 days for the whole year (which month is big and which month is small in a year varies from year to year). Because the average number of days in a year of this solar year is about 1 1 day, and it has accumulated to more than 33 days in three years. If * * = (11* 2)+3or4 = 25th or 26th, a leap month can be set, then 19 sets 7 leap months (that is, the number of days in the solar calendar is equal to the number of days in the lunar calendar). ), there are 383 or 384 days in a year with leap months, and a solar year is divided into 24 solar terms according to the position of the sun, which is convenient for farming. Heavenly stems and earthly branches is used to match the calendar year, and it repeats every 60 years. According to legend, the China calendar began in the Xia Dynasty in China, so it is also called the Xia calendar. Compared with the current calendar, it is also called the "old calendar". It is generally believed that the lunar calendar is suitable for farmers' farming, also known as the "lunar calendar". It is impossible for the lunar calendar to have two leap months in a year, and it is impossible to have leap months for two consecutive years.