It's not often that people get a glimpse of the largest animal that has ever lived. But rare drone footage of a blue whale mother and her calf gliding through the Southern Ocean off Antarctica has gone viral this week.  

The footage was shot in late January by members of the activist group Sea Shepherd Society, who are patrolling the area in the ship Steve Irwin to deter poachers.  

"This is nice footage, and what makes it interesting is that Antarctic blue whales have a low density and are hard to see and study," says John Calambokidis, a National Geographic explorer and research biologist who studies the animals with Cascadia Research in Washington state.

Highly endangered, blue whales can