Dog days are the hottest time of the year, and the old saying "summer solstice will be in ambush", which refers to the dog days that start on the third day after the summer solstice solar term every year.
This year's (2024) summer solstice solar term time is June 21, and the third Geng day after the summer solstice is July 15, according to the saying of "summer solstice three Geng will be ambushed", this year's dog days will start on July 15.
The length of dog days is not fixed, some years are 30 days, others are 40 days. Interested friends may find that in recent years, the dog days have been 40 days every year, and it has been a long time since you encountered a 30-day dog day.
This year's dog days are still 40 days, but there is a little bit of speciality, or something that is different from the 40 days in previous years, where is the specific performance?
Why are dog days divided into 30 days and 40 days?
The calculation method of dog days is based on the ancient Ganzhi day method, and the 10 heavenly stems are matched with the 12 earthly branches, forming 60 different groups of names to record the days. Among them, the character "庚" is the 7th character of the 10 heavenly stems, and the Geng day is repeated every 10 days. Therefore, starting from the third Geng day after the summer solstice, every 10 days is a stage until the end of the first Geng day after the beginning of autumn.
Since the occurrence of Geng days is not fixed, the dates of the dog days of each year also vary. In general, the first and last days are 10 days, and the number of days in the middle depends on the morning and evening of the Geng day between the summer solstice and the beginning of autumn. If there are 4 Geng days between the summer solstice and the beginning of autumn, the middle volt is 10 days, and if there are 5 Geng days, the middle volt is 20 days. Thus, the total number of dog days is 30 days in some years and 40 days in others.
What's special about dog days this year?
If you look at the total number of dog days in recent years, you will find that it has been 40 days for 10 years, and the last dog days were 30 days, and it goes back to 2014, that is, from 2015 to 2024, the total number of dog days is 40 days.
And by next year, 2025, the total number of dog days will "finally" usher in 30 days. Therefore, this year (2024) dog days are the last year of this 10-year 40-day dog day, and this is the special point of this year's dog days.
There is a folk saying that a year with dog days of 30 days is called "dog days", and a year with dog days of 40 days is called "dog days". This year is the last year of the transition from dog days to dog days for 10 consecutive years, and that's what makes it special.
Is a 40-day dog day necessarily hotter than a 30-day dog day?
Many friends will think that the more dog days, the hotter dog days will be, after all, 40 days is 10 days more than 30 days, no matter what, 40 days will be hotter than 30 days.
In fact, according to astronomical experts, this answer is not accurate, and it is possible that 30 dog days will be hotter than 40 dog days.
The degree of heat on dog days is not related to the total number of days, but is determined by various meteorological factors such as the location of the subtropical high, the intensity of sunlight, and the surface humidity.
For example, if a summer is controlled by a strong subtropical high or is affected by warm and humid air currents, even if the dog days are only 30 days, persistently hot and humid weather may occur. Conversely, if the summer is affected by cold air or typhoons, even the 40-day dog days can be relatively cooler.
In addition, geographical factors such as topography, ocean, vegetation, etc., will also have an impact on the temperature of dog days. For example, in coastal areas, dog days may be cooler due to the regulation of the ocean. In inland areas, especially deserts or plateaus, dog days may be warmer due to the small surface heat capacity and large temperature difference between day and night.
This year's dog days are on a specific schedule
This year's dog days are 40 days, starting on July 15 and ending on August 23. The specific times are as follows:
First volcanic period: July 15 - July 24, a total of 10 days;
Mid-volt: July 25 - August 13, a total of 20 days;
Last day: August 14 - August 23, a total of 10 days.
This year is the last year of the 40-day dog days in the past 10 years, and the dog days will be 30 days next year.