Space, as we all know, is big. In fact, it's more than big; it's vastly, hugely, mind-bogglingly big.

But how big is that, exactly, and how do we go about assigning actual, quantifiable distances between planets, nebulae, and other cosmic entities? In this beautifully animated video, produced by the Royal Observatory Greenwich, astrophysicist Olivia Johnson explains how scientists use something called parallax to gauge the distance between the landmarks of our universe.

The film comes via "Measuring the Universe: from the transit of Venus to the edge of the cosmos," a free exhibition currently being held at the Observatory. It's scheduled to run all the way through September 2nd, so be sure to check it out if you find yourself in jolly old England.