Southern hemisphere.
Australia is in the Southern Hemisphere.
southern hemisphere
The Equator.
It's in all of them except the northern one.
Yes, it is in the Northern Hemisphere
Australia
the 21st of june
southern
Australia and Antarctica
That would be a circle composed of two semi-circles: One is the Prime Meridian, the other is the meridian of 180° longitude, directly opposite the Prime Meridian. Each of them connects the north and south poles.
All of it can be found in the southern hemisphere, half of it in the eastern hemisphere, and the other half in the western one.