What is the first day of winter in the southern hemisphere

June has the shortest day in the Southern Hemisphere

it is day in the southern hemisphere because the earth is at a 23 degree angle. the northern hemisphere is in night time.

The winter solstice (shortest day) of the northern hemisphere is simultaneously the longest day (the summer solstice) in the southern hemisphere.

The southern hemisphere summer solstice, falls between December 20 and December 23 inclusive.

Because the 31st of August is the last day of Winter in the Southern Hemisphere.