This was a gorgeous and easy project from Kathy's AngelNik Designs. Kathy seems to be one of those art teachers who posts rarely, but everything she does post is a gem!
The sky is all chalk pastels.
You start with covering the sky with dark blue.
Then you draw swirly lines in medium green and blue. Moving dark to light, draw swirly light green and blue lines over the medium lines.
Add a bit of red near the top.
The green and blue are from excited nitrogen atoms (wheeeee!). The red is from oxygen, which is rarer because it takes much more energy to fluoresce.
Next gently blend the lines with your finger, finishing with brushing the light upwards.
Lastly add a few stars with oil pastel.
Beautiful! And fast, which means you can do several and experiment with different auroras.
We are also watching Frozen Planet, and I have a snowflake project planned. We'll see if I get to it!