I'm on a speculative biology train right now by binging videos on world building and speculations on what said worlds' life and their evolution would be. Thus I want to attempt at making my own planetary system and zooming in to the habitable world that will be the focal point for most of the posts I make here as I speculate on the radiation of the life on that planet until it reaches a state comparable to when the first recognizable civilizations arose on our own planet. Think Mesopotamia or the Indus Valley Civilization. Fair warning, there will be maths involved, but I'll keep all that stuff in spoilers for those who wish to skip it. Oh and terminology, which won't be spoilered.
Before we can reach that point, though. We have to zoom out and move backwards in time. Long before the civilized peoples of this planet, before life crawled out of the waters and onto land, and even before the planet had formed, before even its star had formed. We'll find ourselves looking into our planet's home galaxy.
The Galactic Family:
So, our home planet's galaxy is part of a Compact Group consisting of 7 visible galaxies from our planet's surface and dozens of smaller dwarf galaxies that are invisible to the naked eye from our planet's surface. This group is known as the Striking Blade Cluster due to the positioning of its members. Six of the seven visible members are positioned in such a way that they appear to make the shape of sword, with the first five members at either edge and the six creating a point on one end. Two of these members; the tip and bottom one, are in the process of merging with the seventh and largest member of the group, causing massive amounts of star formation that give the appearance of the "blade" formation "striking" it. Later civilizations will name these galaxies after mythical deities, though the merging galaxies will be known as "Heaven" due to the constant star formation and supernovae from the region. The home galaxy will become known as Guardian, due to its position near at the end of the "blade," where a guard would normally be found.
Guardian itself, other than having an arguably better name than "Milkyway," isn't particularly exciting, which is good. It's smaller than the Milkyway, clocking in at about 88% its mass and around 100kly in diameter. It's what's known as a grand design spiral galaxy, similar to the Whirlpool Galaxy. Guardian has 5 satellite galaxies around it, each named after different mythical heroes.
And that's all that's necessary to know about our planet's home galactic group. Not a whole lot of math or terminology really needed for this section, as Guardian itself isn't a part of the galactic merger happening in its group, and thus wouldn't be subject to the enormous amount of radiation from such a merger. The next post will be about our planet's star and its position within Guardian, and the processes that led to its star's, and its own, formation.