Galactic year

The orbit (white) of the sun (yellow) around the galactic center (GC) together with the widely scattered swarm of those stars (red) that happen to be in the vicinity of the sun. The back calculation over 250 million years is based on measurements of the own movements in the last 15 years.

A galactic year ( GJ ) denotes the complete orbit of the solar system around the center of the Milky Way . Its duration is now generally assumed to be around 225 million years.

The name was first used in 1952 by the Russian astronomer Pawel Petrovich Parenago in a work on the mass distribution in the Milky Way system.

Connection with extinction of species

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Attempts by paleontologists to explain patterns in the frequency distribution of species extinctions with galactic orbits were facilitated by the fact that the astronomers were initially only able to roughly determine the value for the galactic year and there was therefore scope for random matches. Since infrared astronomy has made it possible to see the galactic center, its apparent movement against the background of distant galaxies has been used to determine the orbital period of 250 million years, which has disproved a number of assignments.

There is also no reason why catastrophes should occur with this or half the period, because the sun does not simply move on an inclined orbit plane twice per orbit through the galactic plane, but it oscillates up and down much more often - the figures for the half period are between 30 and 40 million years ago. But some paleontologists now believe to find this period in their data as well.

Lapse of time in galactic years

In this list, GJ = 225 million years.

• 0 GJ : The sun is created
• 4 GJ : The oceans are created on earth
• 5 GJ : The first forms of life arise on earth
• 6 GJ : Prokaryotes arise
• 7 GJ : Bacteria arise
• 10 GJ : continents emerge
• 13 GJ : Eukaryotes arise
• 16 GJ : multicellular cells arise
• 17.8 GJ : Cambrian explosion
• 19 GJ : Perm-Triassic limit (mass extinction)
• 19.6 GJ : Cretaceous-Paleogene limit (K / P impact, dinosaur extinction etc.)
• 19.999 GJ : Modern man (Homo sapiens) appears
• 20 GJ : Today

supporting documents

1. ↑ Geologic Time Scale - as 18 galactic rotations , therein 1 GJ = 250 million years, which is why the values ​​here were converted.