On or around June 21 each year, the rays of the sun will be perpendicular to the Tropic of Cancer at 23°30′ North latitude. This day is the summer solstice in the Northern Hemisphere.

On this day, the earth’s “circle of illumination” will be from the Arctic Circle on the far side of the earth (in relation to the sun) to the Antarctic Circle on the near side of the earth. The equator receives twelve hours of daylight, there’s 24 hours of daylight at the North Pole and areas north of 66°30′ N, and there’s 24 hours of darkness at the South Pole and areas south of 66°30′ S.

June 20-21 is start of summer in the Northern Hemisphere but simultaneously the start of winter in the Southern Hemisphere.

It’s also the start of other things too..