Why is the Millennium the biggest temperature difference between day and night in the northern hemisphere?

Every year around September 7th in Gregorian calendar, when the sun runs to 165 degrees, it begins to enter the Millennium solar term. The Millennium is a typical autumn solar term, and the temperature drops rapidly. At night, the temperature has reached the condition that steam condenses into dew. The dew in the field is crystal clear in the morning, and it is named Bailu because the dew turns white.

The biggest temperature difference between day and night in the northern hemisphere is not just the day of the Millennium, but the day when the Millennium is hotter than the previous period, but it is obviously cooler in the morning and evening, which is the characteristic of the Millennium solar terms. The Millennium solar term is the solar term with the largest temperature difference between day and night throughout the year. In more than ten days of this solar term, the temperature difference between day and night is generally between 10℃ and 15℃. Especially in the morning and evening, it is very cold, so you should wear more clothes. As the saying goes, "Don't expose the dew in midsummer" and "The dew falls at the autumn equinox, and it is cold all night", which means that the temperature drops rapidly at night, so we should pay attention to keeping warm.