The beauty of festivals · Beginning of Summer丨When is the beginning of summer and how is it determined?

After welcoming the beginning of summer on May 5 for three consecutive years, this year it will be on May 6. Astronomy experts said that the beginning of summer on the 6th is relatively rare, with only 9 such events in the 100 years of the 21st century.

The Beginning of Summer is the seventh solar term in the twenty-four solar terms and the first solar term in summer. Together with the Beginning of Spring, the Beginning of Autumn and the Beginning of Winter, it is known as the "Four Beginnings", representing the change and transition of seasons.

(Copyrighted image from the gallery, no permission to reprint)

Yang Jing, a member of the Chinese Astronomical Society and director of the Tianjin Astronomical Society, said that there are two solar terms in each month of the Gregorian calendar, which fall on the 6th and 21st of each month in the first half of the year and on the 8th and 23rd of each month in the second half of the year, with a difference of one or two days. As for the Beginning of Summer solar term, its date in the Gregorian calendar year will only change on May 4th, 5th and 6th. In most years, it falls on the 5th, followed by the 6th, and the least is the 4th.

The astronomical almanac of the 21st century shows that the Beginning of Summer falls on May 5 83 times, on May 6 9 times, and on May 4 8 times. Among them, all the years with the Beginning of Summer on the 6th are concentrated in the 31 years from 2001 to 2031, which means that there will be no Beginning of Summer on May 6 in the 69 years from 2032 to 2100.

Many people will find that each solar term is accurate to the time and minute and is different every year, even for the same solar term. Take the Lixia in 2020, 2021 and 2022 as an example. Although they are all on May 5, the specific time of the solar term is different, at 8:51, 14:47 and 20:26 on the 5th. "This is the result of the Earth's non-uniform speed around the sun," Yang Jing explained.

As the only institution in my country that specializes in the study of almanac astronomy and the compilation of calendars, the Purple Mountain Observatory compiles the lunar calendar for the following year according to the corresponding calendar calculation method, including the time of the solar terms, which is accurate to the minute. It is officially published as a standard in the annually published "Chinese Astronomical Calendar" and released to the public in the form of "Calendar Data". According to the authoritative calendar released by the Purple Mountain Observatory, the exact time of the beginning of summer this year is 2:19 on May 6.

Yang Jing said that the solar term is a physical moment, but due to the different time differences in different places, the local time of the solar terms in different places is not the same. However, since our country stipulates the unified use of Beijing time, the solar terms across the country are at the same time and moment.

Produced jointly by Xinhua News Agency Domestic Department and Xinhua News Agency Tianjin Branch