Starts With A Bang

Ask Ethan: Why are maps of the cosmos oval-shaped? (Synopsis)

Image credit: ESA and the Planck Collaboration.

“The bedrock nature of space and time and the unification of cosmos and quantum are surely among science’s great ‘open frontiers.’ These are parts of the intellectual map where we’re still groping for the truth – where, in the fashion of ancient cartographers, we must still inscribe ‘here be dragons.'” -Martin Rees

We know the Earth is an almost-perfect sphere, yet maps of it always stretch it down to a two-dimensional surface. Outer space, too, when we look at it, offers views that extend deep into the cosmos in all directions, also on a sphere. But if you want to make a map of the Universe, you must stretch it down to a two-dimensional surface, too.

Image credit: Axel Mellinger’s All-Sky Milky Way Panorama 1.0 (2000).

These maps are almost always shown as oval-shaped, but there’s a good reason for this! You cannot show, simultaneously, a two-dimensional projection of a sphere that is simultaneously: connected, area-preserving, free of shape-distortion, and where latitude and longitudes appear perpendicular. You can pick three at most, and the projection most frequently chosen for space, the Mollweide projection, is very different from the Mercator projection chosen for Earth.

Image credit: ESA and the Planck Collaboration, of the CMB in a Cartesian frame, distorting the areas around the poles significantly.

Go get the full story — and see some amazing possible visualizations — on this week’s Ask Ethan!