The circle of illumination just touches (but does not illuminate) the antarctic circle on or about June 21. The Earth is tilted, and this tilt leads to the southern and the northern part of the Earth having the day length variation. June, 20-22, is considered the summer solstice, where the length of the day in the northern hemisphere is longest whereas in the southern hemisphere it is the shortest. During this period, the circle of illumination or the rays from the Sun, barely touch the Antarctic circle. This causes darkness and night in Antarctica.
