Major Heat (Dashu in Chinese) is the 12th solar term of the Chinese lunar calendar. It begins when the Sun reaches the celestial longitude of 120° and ends when it reaches the longitude of 135°. It more often refers in particular to the day when the Sun is exactly at the celestial longitude of 120°. Similar to Minor Heat, Major Heat is also a solar term that reflects the heat of summer. Major Heat means extreme heat. During Major Heat, most parts of China enter the hottest season of the year. It is an important period for the growth of crops. Many natural calamities such as floods, droughts and typhoons also happen frequently in this period.

According to astronomers, the reason why the weather in Major Heat is so hot is that the heat absorbed by the earth during the day is much more than that radiated at night. Thus the heat has been accumulating day by day and reaches its peak in Major Heat period. Generally speaking, for southern China, Major Heat is the period with the most sunshine, highest temperature and plenty of rainfall.