aurora australis; southern lights
Refers specifically to the southern polar lights, as opposed to 北極光 (aurora borealis).
The aurora australis is an aurora that can be observed in the Southern Hemisphere.
オーロラ is the general loanword for aurora, encompassing both northern and southern lights. 南極光 is a more technical, kanji-based term.
Compound of 南極 (South Pole) and 光 (light), directly describing the southern polar lights.