Worldbuilding Wednesday 5/1/24: Let’s Talk About the Milky Way (Part 2)

The Birth of the Milky Way (1668) by Peter Paul Rubens

The painting above, by Peter Paul Rubens, offers a different take on the Milky Way’s origins. I like it a lot better than Tintoretto’s which appeared last week. For one thing, it feels more real. There’s a story being told as your eye travels from element to element in the painting. But it’s not the same story as Tintoretto’s. It’s more direct and less busy. In Rubens’ painting Hera suckles baby Heracles  willingly as Zeus fumes at her back, a bundle of lightning bolts at his feet, annoyed he isn’t paying attention to her. Heracles looks amazed at the size of Hera’s boob and so misses the stream of milk she squeezes, which turns into a glowing cloud at the lower left of the picture. In contrast, Tintoretto gives up just a few measly stars.

In addition to the cloud, Heracles and Hera are lowing with light, bringing them to front and center of the composition. In a nice touch, the dark shapes of Hera’s peacocks, which she uses to draw her chariot, look like the dark clouds in the center of the Milky Way that, in less light-polluted times, were more visible.

Like the myth, a planet’s view of the Milky Way can change depending on where it is placed and the tilt of its axis.

First, some basic astronomy.

Earth’s view of the Milky Way looks the way it does because our solar system is embedded within it. Picture it as a flattened disk made of glowing dust. We are inside that disk, approximately halfway from its center to its edge. Now picture the disk as having multiple arms of dust like a hurricane’s clouds as seen from above. We are located at the inner edge of one of the two main arms inside a smaller trailing arm called the Orion Arm, or sometimes Orion Spur. This pic from the European Space Agency shows it in a simplified way.

 

So, let’s posit we are floating in the galaxy like the hamster at left, in the same position our solar system is in (let’s pretend the sun isn’t there for now.) Looking inward would give us a view of the Milky Way’s glowing core. Doing a 180 degree turn and looking in the opposite direction we would see the glowing outer arms. Looking to either side we would see the far-off point where they appear to connect and meet because of perspective. Positioned this way we would appear to float at the center of a faint but giant ring.

Of course, in real life dark clouds of interstellar dust would obscure most of the view, and the albedo – the brightness – of the galaxy wouldn’t be very high, certainly not as high as it appears in long exposure photographs from Earth telescopes. The photo below, a casual one snapped from a window in the ISS, is more of what you’d see with your own eyes.

The wonderful thing about writing speculative fiction, however,  is that you can ignore all this. You can invent your own galaxy and have it be as bright and unobscured as you please.

If your theoretical home planet was in the position where you are floating in your spacesuit, with its axis pointing in the same direction as your Milky Way analogue’s axis, the view from the planet would be different. Those on your planet’s equator would see a glowing arch across the sky that moves from east to west like a panopticon, while those near the north or south poles would see it on the horizon like a foaming sea. In between those latitudes, the position would vary from high to low in the sky, but remain constant through the night. It wouldn’t appear to spin around the night sky like Earth’s Milky Way does. (I’ll get to that later.)  I’ll call this one the carousel position, because the planet’s axis is that of a pony on its pole moving around the galaxy’s axis which is the carousel’s central support.

In this setup, cultures at the high latitudes, where the home galaxy view sits on the horizon, might reference it as a sea, lake, river, or beach. Some might take it as an actual feature of the land, like a ghostly mountain range. This is assuming, of course, there’s a clear view of it and no light pollution. The skies of a fantasy world might have gegenshein, zodiacal light, aurorae, or other features that obscure it; OTOH, it might be brighter or larger than the Milky Way so it’s super visible. It’s up to you.

At the equator the impression would be of an arch, road, or river fixed at the very apex of the sky, moving east to west as the night progressed. I can guess the impression on the world’s mythology would be much stronger than ours, because it would actually seem to connect some distant place on the horizon to another.  The same could be said for cultures in the middle latitudes.

Now, what would happen if your planet’s axis pointed into the center of the your galaxy, so it’s rolling along the galactic disk like a marble in a curved groove?

Those at the poles would see an arch that rotates through the night like the hands of a clock, while those at the equator would see nothing, or at the most a slight starry haze at direct north and south. Those in between would have the clocklike view with the center of the clock, where a theoretical pole star would be,  in the midst of the disk. This would make it very easy for culture’s to mark the passage of time, in the night at least. If you’ve got an exceptionally luminous galaxy, in the day as well.

An arrangement like this would have notable differences in the view between the northern and southern hemispheres. One hemisphere would have a view of the brighter, glowing core, while the other would not.

More home galaxy names

I hope I haven’t been too theoretical with this and confused anyone too much. There’s much more to say regarding a planet’s view of its home galaxy, chief of which is its relation to its sun.