Why is it currently summer in Australia?

Answer 1

Due to the tilt of the earth's axis there is always one pole angled away form the sun, and one angled toward the sun, except at the equinox when they are balanced. When the North pole is angled away from the sun the northern hemisphere experiences winter, simultaneously the South Pole will be angled toward the sun so the Southern Hemisphere experiences summer. Likewise when the north pole is angled toward the sun then the situation is all reversed.