On May 5， 2016， China National Philatelic Corporation issued a set of six first-day covers carrying a set of six special stamps titled “The 24 Solar Terms（II）” with a total face value of 7.20 yuan. The pictures on the stamps are titled“Lixia”， “Xiaoman”， “Mangzhong”， “Xiazhi”，“Xiaoshu” and “Dashu”， respectively.

A Chinese saying goes that “spring is the season for crops to sprout， summer for crops to grow， autumn for harvest， and winter for storage.” Plants grow fast in summertime. According to Collection of Annotations to the 72 Pentads， “li means start； xia （summer） is the time when crops grow up.” Therefore， emperors would lead officials to the southern suburb of the capital for a ceremony welcoming the arrival of summer and praying for harvest on the day of Lixia （Beginning of Summer） in ancient times.

Starting from Xiaoman （Lesser Fullness of Grain）， seeds of summer-harvested crops in northern China， such as the winter wheat， begin to become full. According to Collection of Annotations to the 72 Pentads， “Xiaoman is the time for grains to become full.” Upon the arrival of Xiaoman， the majority of Chinese territory enters summertime in a meteorological sense. Due to high temperatures and enhanced atmospheric convection during Xiaoman period， large-scale frontal precipitation is gradually replaced by local convective thundershowers.

Mangzhong （Grain in Ear） is the third solar term in summer. As recorded in Collection of Annotations to the 72 Pentads， “Mangzhong， a solar term in the fifth lunar month， marks that people can sow seeds of crops.” During Mangzhong period， summer-harvested crops such as the winter wheat are ripe and ready for harvest， and farmers begin planting crops that are harvested in autumn. Crops sowed in spring and harvested in autumn need careful tending in the period， just as a folk saying goes， “from late May to mid-June every year， farmers are busy with harvesting the crops by making full use of every minute.”

In summer， trees turn green and lush， and daytime becomes longer. Xiazhi（Summer Solstice） sees the longest daytime in a year. On that day， the sunshine duration lasts as long as 17.1 hours in Mohe County， Heilongjiang Province， at the northernmost end of China. According to the Transcript of Following the Rules， “when the sun moves to the northernmost point， the daytime becomes the longest； the day is thus called Xiazhi. Zhi means zenith.”After Xiazhi， the solar heat reaching the earth surface decreases with each passing day， hence the ancient Chinese saying “yin begins since Xiazhi.”

According to Collection of Annotations to the 72 Pentads， “shu means heat， and there are Xiaoshu （Slight Heat） and Dashu （Great Heat）； Xiaoshu is in the beginning of the month， while Dashu in the middle. It isnt extremely hot during Xiaoshu.” Therefore， as a folk saying goes， “the extremely hot weather doesnt arrive during Xiaoshu， but the dog days arrive during Dashu.” In Xiaoshu period， the distribution of rain and drought in eastern China changes substantially. For areas on the middle and lower reaches of the Yangtze River， the rainy season comes to an end， and the summer dry season begins； for northern China， the dry season ends， and the summer rainy season starts.

A folk saying goes that “the coldest weather occurs in the third nine-day period after Winter Solstice， and the hottest days arrive in the second of the three ten-day periods of the hot season.”The hottest ten days are just in the period of Dashu. In the period， the highest average temperature appears in Turpan， northwestern Chinas Xinjiang Uygur Autonomous Region. Yet， the hotness isnt unendurable due to the dry air there. Despite their relatively lower average temperatures than that of Turpan， the areas in the middle and lower reaches of the Yangtze River are unendurably scorching and suffocating in mid-summer， as if one stayed in a steamer. Hence， the three cities known as “Three Stoves”are all located in the region.