Worldbuilding Wednesday 5/8/24: Let’s Talk About the Milky Way (Part 3)

Marduk had two pairs of eyes and four ears and flames shooting from his mouth, a rather off-putting deity if you ask me. Tiamat is depicted as a not unusual dragon.

The Greeks weren’t the only ones to create origin stories for the Milky Way. Centuries before them, the Babylonians had their own version: it was the tail of Tiamat, the dragon/serpent goddess of primordial chaos, placed there after her defeat by the god Marduk. Likely the first version of the chaos vs. order megamyth, not to mention female vs. male.

In my last post I talk about the different views a planet might have of its home galaxy, assuming it was the same as Earth’s. Today I’ll continue the discussion.

What if the planet was closer to its galactic core? In the conjectural view above the night sky is crowded with stars, so crowded that even without a moon it would never be completely dark. The band or path would be much wider than the Milky Way’s too, it might even cover the entire sky. Figure this in with the tilt of the axis of the planet and the inhabitants would mythologize it very differently.

If the home planet were farther out, the band would be thinner looking into the core, and looking outward, almost nonexistent… that is, if the planet was still embedded inside the arms like Earth is. If the planet was in its halo of stars, removed from the arm and looking down, the view would be more spectacular.

Again, depending on the planet’s tilt and one’s location, one would see all of it, some of it, or none. Looking in the opposite direction from the galaxy, there’d be a few scattered halo stars, and that’s it.  On might be able to see other distant galaxies, though!

This is a good time to answer the question of why Earth’s view of the Milky Way is so messed up.

This useful graphic from fizixfan shows the tilt of the sun’s ecliptic (the plane in which all the planets orbit around it) and the earth’s tilt in relation to the Milky Way, which is aligned horizontally. There’s a lot of info packed in here, but it is clear to see that Earth is neither in the carousel or the marble-rolling position I wrote about in the last Worldbuilding Wednesday. Its axis is pointing at an almost 45 degree angle compared to the Milky Way’s up-and-down orientation. When you figure in its tilt in relation to its position around the sun, that dictates which parts of the Milky Way can be seen or not seen through the seasons and why it seems to wander all over the night sky. It’s why some parts can’t be seen from the Northern hemisphere, and vice versa.

But astrophysics has an answer to that, too. The Earth wobbles on its axis like a spinning top. so the pole stars change position over the years, forming a circle every 25,770 years. When the ancient Egyptians built the pyramids, the North Star was Thuban; many centuries from now, Vega will become the closest and so wear that title. That means what parts of the night sky are visible will change too. Over time, Orion will lower on the horizon of the Northern hemisphere while the Southern Cross will rise.

The southern hemisphere isn’t as lucky when it comes to pole stars. There currently isn’t one. But that will change in ten thousand years’ time.

Diagram showing precession around the North and South celestial poles. Candidates for future pole stars are named, based on the brightness and proximity to the precessional path. (Celestial north/south is in the center.)

In the diagram above (click to see larger) the current year is +2000. Yes, I know it’s 2024, but a few years don’t matter on the celestial scale. The negative numbers are in the past, the positive ones, the future. When the cycle completes and starts again, the star positions will be slightly different, because all the stars, and the sun itself, are moving. Millions of years from now, there may be a whole new pole star we haven;t met yet, because it hasn’t moved into our solar neighborhood.

But, when if your setting is on a world that is not Earth, who says your home galaxy has to look like the Milky Way at all?

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