In the vast expanse of the cosmos, the Milky Way Galaxy is our home.
You’ve no doubt seen images of the Milky Way and similar galaxies elsewhere online. It’s a large, spiral galaxy, one of the most spectacular galactic shapes. That spiral shape is fairly iconic–and for years, that’s as far as I thought galaxy classification went.
Turns out, galaxies are way more diverse than just the main three classifications I knew about (spirals, ellipticals, and irregulars). The Milky Way is fully classified as an SBbc: a barred spiral galaxy with a medium-sized nucleus.
Spirals are also described as “grand design” (two distinct spiral arms) or “flocculent” (a sort of fluffy appearance); the Milky Way is somewhere in the middle.
But even those classifications and descriptions don’t fully describe our galaxy.
So what exactly is the structure of the galaxy we call home?
Consider that we can’t really take a photo like this of our galaxy. We’re inside it, and space travel has not advanced to the point where we can leave it just yet. There’s no way we can get a camera out to take a picture from this perspective.
Most things in the universe–like stars, planets, and even other galaxies–can be measured using their angular diameters. That is, we use trigonometry to find their actual sizes based on how large they appear to us in the sky.
But that doesn’t work for an object that we’re inside of.
In order measure the size of our own galaxy, early astronomers had to get a bit creative–with variable stars.