If you get away from city lights and witness the astonishing beauty of the night sky, most of the stars you can see are part of what is known as the “main sequence”. The few that aren’t part of it get attention out of proportion to their numbers, but sometimes we should step back and consider the stars that make up most of the galaxy, our Sun included.

Previous explainers have answered the question of what K-type and B-type stars are, in both cases also looking at why they matter. Both of these are subclasses of the broader category, main sequence stars.

The galaxy was once nothing but a vast cloud of hydrogen, a little helium and lithium, and almost certainly lots of dark matter. Where the gas was densest, gravity drew in more material, and caused that density to increase in an initially self-sustaining process.

Eventually, the density reached a point where something happened that would take our breath away if we were not so familiar with its outcome: fusion ignited. So much gas became concentrated in a small area that the gravitational force became large enough to overcome the electrostatic repulsion between protons, and there was light.

The same process occurred at millions of locations across the galaxy, sparking the first stars.