I always wonder how to create an aurora or nothern lights brush in photoshop. I bought a japanese tutorial painting book, which sort of show how to make it, but it is using a squash gradient triangle which doesn't give the result that I really want. So, I experiment a bit and found a blur vertical shape is the solution.

Aurora Polar Lights Brush Creating Tutorial:
https://youtu.be/_sGqm5KRgvA

Painting Timelapse Video:
https://youtu.be/j4Mn_p2eqEI