Find a seat on the side of the aircraft opposite the sun.     Search the clouds where the shadow of the aircraft would be – the antisolar point.     The glory is a delicate shimmering pattern of concentric coloured rings that drifts along the clouds with the airplane sometimes shrinking or swelling as it does so.

It is a diffraction pattern produced by light interacting with small cloud droplets and being scattered almost directly backwards.    
 
Not all cloud decks produce glories.   Almost monosized droplets produce the best with a dim central glow surrounded by rings tapering off in brightness.    

At left is a Mie theory simulation of glories computed by IRIS.    One half is for monosized droplets, the other for a droplets with a 20% (standard deviation) spread around the mean diameter of the population.  

A range of drop sizes smear away the glory structure because the diffraction pattern is drop size dependent – smaller drops give large glories and vica-versa.