The Year of the Dragon, a 354-day year, is 30 days less than the previous year's Year of the Rabbit. Yang Jing, a member of the Chinese Astronomical Society, explained that the lunar calendar is a traditional calendar in China, which comprehensively considers the movement cycle of the moon around the earth and the earth around the sun, so it is a lunisolar calendar. The average length of a lunar month, the synodic month, is 2953 days, but for convenience, it is sometimes prescribed as a small month of 29 days, and sometimes a large month of 30 days.
If the lunar calendar is fixed at 12 months per year, then the length of the year will be 354 or 355 days, which is a big difference from the 365 or 366 days in the return year. This gap accumulates for more than one month in three years, resulting in serious inconsistencies between the year, month and season of the lunar calendar. To bridge this gap, the lunar calendar employs the method of setting leap months. Every two or three years, a month is set as a leap month, and such a year is called a leap year, which consists of 13 months and a total of about 384 days. A year without a leap month is called a common year and has only 12 months.
As for which month is set as a leap month, it is determined according to the 24 solar terms. In the 19 lunar years, there are usually 12 ordinary years and 7 leap years, which is what we often call "19 years and 7 leap years". This setting makes the average length of the lunar year roughly match the average length of the return year.
Yang Jing also pointed out that the Year of the Rabbit is a leap year, and it has a "leap February", so there are 384 days in the year. The next Jiachen Dragon Year is a common year, with only 354 days. This means that compared to the Year of the Rabbit, the Year of the Dragon is 30 days shorter. In addition, the Year of the Snake in 2025 is another leap year, which has a "leap June" and the year is also 384 days. Therefore, compared to the Year of the Snake, the Year of the Dragon is also 30 days less.