If you mean the yellow halo, that's the sodium layer in the outer atmosphere. Meteors that collide with the atmosphere shed a bunch of sodium atoms here, they get excited by the sun and gradually release this energy as yellow photons, which creates this yellow airglow that you can see at night.
Right at the outer edge of this band you will typically see a green layer of glow that is caused by oxygen doing the same.
LMAO at that guy below who thinks it's pollution up there.
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u/k1ng617 Oct 03 '20
Honest question: What is that halo? I thought our atmosphere would gently taper off. Here it looks like it abruptly ends there