Begin of the holy month of Ramadan.
Chinese Muslims or Hui people 回族 can be found all over the Yunnan province. They often live in separate villages as cultural taboos have kept intermarriage with people of other religions relatively low.
The Muslim calendar is strictly a lunar calendar, which means that Muslim holidays circle through the seasons as every lunar year has less days than the solar year. In addition, the exact timing of Muslim holidays can depend on the actual visibility of the moon, so the dates for any given Muslim festival might vary by one day and are sometimes just decided early in the morning.
The fasting actually begins the evening before at sunset.
Please note that islamic holidays are difficult to compute, so this day might be wrong by a day. Please check.