Inversion:

Today was a beautiful day outside. 45 degrees and no wind. It was so nice that I spent part of the day on the front deck. 

It is rare that we can see a temperature inversion as clear as tonight. We all know that cold air sinks and warm air rises. The temperature this evening dropped quickly as the cold air descended. It forced the warm air up and hence the bright blue and pink on the horizon.  

As the cold night air sinks we can see the separation of the different air layers out our front window.