Is the summer solstice a lunar or solar calendar?

Summer solstice is one of the 24 solar terms, which occurs on June 2 1 or 22 of the Gregorian calendar every year. On the day of summer solstice, the sun moves to 90 degrees of the yellow meridian (summer solstice, currently in Gemini), and the position where the sun directly hits the ground reaches the northernmost point of the year, almost directly to the Tropic of Cancer. At this time, the daylight hours in all parts of the northern hemisphere reach the longest in the whole year. For the Tropic of Cancer and its northern area, the summer solstice is also the highest day of the year at noon. During the summer solstice in Beijing, the daytime can be as long as 15 hours, and the height of the sun is as high as 73 32' at noon. On this day, the northern hemisphere received the most solar radiation, almost twice as much as the southern hemisphere.