On the 21st at 12:51 for example in Spain astronomical summer begins, it is the day of the solstice.
The word solstice refers to the apparent stillness of the sun for a few days starting on the 21st, both the summer solstice and the winter solstice have had magical connotations since the most remote times.
3 days after the summer solstice, the feast of Saint John is celebrated in the northern hemisphere, in the northern hemisphere which contains 90% of the world's population, the sun reaches its highest point, and from that day it declines and resurges at the winter solstice, in the southern hemisphere it is just the opposite, for those of you reading this from the southern hemisphere I leave this link here.
When the Sun is at its highest point, bonfires are lit, its meaning is often purifying, that special day when the Sun the king and lord of all celestial bodies, is illuminating the greatest possible extent of territory also served ancient shamans to make their spiritual light span the entire globe.
Christmas is 3 days after the winter solstice, the feast of Saint John is 3 days after the summer solstice, why 3 days difference?, because it is the time in which the sun appears to be still, and that is precisely the meaning of solstice.
I leave you the video about the position of the planets and astronomical events of the month of June