The dog days refer to the three "crouching" periods in the summer of the lunar calendar, namely, the initial crouching, the middle crouching and the last crouching. The first fall is usually from the end of June to the beginning of July, the middle fall is from the middle of July to the beginning of August, and the last fall is from the middle of August to the end of August.

Among the three volts, the midvoltage is considered to be the hottest volt. This is because the sun shines directly on the ground for the longest time and the temperature is relatively high during the midsummer period. In many areas of China, the temperature often reaches its peak during the mid-summer period, which is called "hot summer".

However, the specific temperature and heat will also be affected by geographical location, climatic conditions and years, so the hottest volt may be different in different regions and years.