Trying to see the Milky Way in 3D

One of my favourite things to do is to try to perceive the three-dimensionality of the night sky, especially the Milky Way and our place inside that incomprehensibly huge whirpool of stars. It’s a weird act of faith and imagination, because although we actually are inside that disc of gas and stars, it does not and cannot actually look much like it. Most importantly, the distance to stars cannot be perceived directly, only known as an abstraction. So you have you have to pretend to be able to see what is actually there — an inversion of human nature, which is much more inclined to pretend to see what is not actually there.

A home like ours. This isn’t our own Milky way, but it strongly resembles it: a particularly gorgeous picture of NGC 6814, a classic “grand design” spiral galaxy. This is a Hubble Photo from ESA/Hubble & NASA, with some processing magic from Judy Schmidt. I found it on APOD.

It’s far easier to imagine the depth with really good dark skies, which I rarely get to see: everywhere I normally go is badly light polluted. And I go to bed early. And the weather often doesn’t cooperate. So the stars rarely align, ha ha, and it’s surprising how rarely I actually get to do this visualization exercise with lots of stars. But when I do, I marvel at how much easier it is to “see” the depth of the sky when there are more stars.

I find it quite hard to achieve the perception of depth, though. It’s like one of those illusions where you can see two different things in the same image, and once your brain has settled on one version it can be really tricky to flip it (but when it does, it’s not subtle). The illusion of dimensionality can pop in rather spectacularly, and it’s extremely rewarding when it does.