How the Dog Days are calculated is as follows:

The specific date of the Dog Days is calculated based on the lunar calendar. Dog Days is a solar term in the traditional Chinese lunar calendar and represents the hottest period of summer. Generally between mid-July and mid-August each year. The lunar calendar is a calendar system based on the movement cycle of the moon. The length of a month is about 29.5 days.

The dog days are determined based on the position of the sun. When the sun reaches 120 degrees of ecliptic longitude, it is the beginning of the dog days. The ecliptic longitude is the angle of the sun relative to the vernal equinox, which moves approximately one degree per day. In order to determine the specific date of Dog Day, calculations need to be made based on the lunar calendar and the position of the sun each year.

This calculation is usually performed by astronomers and calendar experts, who combine calendar and astronomical observation data to determine the date of Dog Day. It is important to note that the date of the Dog Days may vary in different years.

Because the length of the lunar calendar and the solar year are not exactly the same. In addition, the start and end dates of Dog Days may also vary from region to region due to differences in climate and seasonal changes in different regions.

Expand knowledge:

The lunar calendar is the current traditional calendar in China. It belongs to the lunisolar calendar, that is, the combined calendar of the lunar calendar and the solar calendar. It is based on the changing cycle of the moon phases. Each time The lunar phase changes into one month, referring to the length of the solar return year as a year, and adding twenty-four solar terms and setting leap months to make the average calendar year compatible with the return year.

The lunar calendar combines the lunar calendar and the solar calendar to form a lunisolar calendar. Because of the use of "Xia Zheng", it was called the Xia calendar in ancient times. The current lunar calendar was renamed "Xia Li" to "Lunar Calendar" after 1970. The new day is the first lunar day of the lunar month, which means that the first day of every lunar month must be the new day.

Each lunar month reflects a complete cycle of moon phases and therefore belongs to the lunar part of the lunisolar calendar. The twenty-four solar terms in the lunar calendar reflect different positions on the earth's orbit around the sun, that is, the tropical annual cycle, and therefore belong to the solar calendar part of the lunisolar calendar.