Why is Xining still so bright at nine o'clock in the evening?

The reason why Xining is still so bright at 9 o'clock in the evening is because Xining is located in the west of China, about 0/02 degrees east longitude, and also in the East Seventh District. Around the summer solstice, the sun shines directly on the tropic of cancer, and extreme sunlight appears in the Arctic Circle. Therefore, the sunset time will be delayed every day, resulting in the delay of night time. Even at 9 o'clock in the evening, it is still bright. This phenomenon is particularly obvious in summer, and it gets dark relatively early in other seasons.