Aurora - meteorological effect (Unity 5.5 and 5.6)
http://u3d.as/H0L
Aurora is a Unity particle effect library for sale which includes the titular meteorological phenomenon and 17 magical buff/healing effects.
This video demonstrates the meteorological effect in 4 different hues, but it's very straightforward to customize your own color for the aurora.
0:00 Green-purple
1:15 Pale green
4:27 Red
6:10 Blue
Video of magical effects in the same package:
https://www.youtube.com/watch?v=VCovtt3nt_w
More of our assets: http://u3d.as/cxf
HDR bloom is enabled in this demo which can be implemented in your scene with the free image effect from Unity Standard Assets. All required scripts and settings of bloom are detailed in the Aurora package documentation. (Asset Store does not approve unofficial asset contains scripts/shaders from the Standard Asset.)
Bloom effect aside, everything (aurora/cloud/stars/ground objects) appears in this video is included in the package.