Minor Heat has already passed for more than ten days, and in about another week we will enter Major Heat. Then after enduring another month, it will be End of Heat. This period is the hottest time of the year. During this period, the sanfu days that we care about most will also appear. The length of the sanfu days differs each year; in some years there are 30 days, and in others 40 days.

I think what everyone cares about most is how many days the sanfu days will last this year, right?

This year's sanfu days start today, that is, from July 17, 2018, and end on August 25 of the solar calendar, lasting forty days. Do you feel like you are already melting from the heat before the hottest days have even begun? That's right, this year's sanfu days will last forty days, of which the chufu is 10 days, the zhongfu is 20 days, and the mofu is 10 days.

I think at this point you may be curious why some sanfu days last thirty days.

For this reason, I also specifically looked at the length of the sanfu days in recent years, and found that among the sanfu days in the past eight years, only 2014 and 2012 had thirty-day sanfu periods.

In fact, this mainly involves the issue of our country's traditional astronomical calendar, namely the issue of the ten heavenly stems and the twelve earthly branches. There is a saying, "After the summer solstice, count the third geng day as the start of the chufu." People in ancient times used the mutual combination of the heavenly stems and earthly branches to calculate days. In this way, every ten days a geng day with the character geng would appear, so the start time of the chufu is determined, and the fourth geng day after the summer solstice is the start of the zhongfu, so the chufu can be determined as the following ten days. Next is the mofu; the first geng day after the start of autumn is the mofu, and the mofu lasts ten days. Therefore, the zhongfu period in between is uncertain. Sometimes it is 10 days, and sometimes it can be 20 days.

Which fu is the hottest among the sanfu days?

As the saying goes, "Cold is at the sanjiu, heat is at the zhongfu." From this, it seems the hottest should be the zhongfu. Why is the zhongfu the hottest? First, let us look at the issue of heat balance. After entering Minor Heat, the weather becomes hotter and hotter. By the time it accumulates to the zhongfu, the earth's heat balance is already very unbalanced, because the heat from the daytime cannot fully dissipate at night, so by the zhongfu it reaches the peak of heat accumulation, and naturally it becomes so hot that you only want to hide in an air-conditioned room.

In addition, the zhongfu generally falls during the period from mid-July to mid-August. During this time there is a lot of rain, the air does not circulate, and the feeling it gives people is that although it is raining heavily, it is even more stifling and unbearable.

During this period, most regions of our country are dominated by the subtropical high, and within the high pressure descending air currents prevail, the weather is clear, direct sunlight is strong, and the surface heats up even faster.

However, the weather during the sanfu days is hot, so everyone should do a good job of preventing heatstroke. Also be careful not to eat too much cold food, and do not take a cold shower right after sweating heavily; doing so is very bad for the body.

The above comes from Science Agriculture.