2. 365 days a year (366 days in leap year) is not an integer multiple of 10. One day this year is Geng Day, but next year is not necessarily Geng Day. Due to the uncertainty of Geng day, the date of accommodation is different every year. The dog days are the hottest time of the year, which can be divided into three days: the first, the middle and the last. This is because the days are long and the nights are short after the vernal equinox, and the sunshine is close to the direct summer solstice.