The Lion, the Witch, and the Wardrobe
How we cite our quotes:
Every moment the patches of green grew bigger and the patches of snow grew smaller. Every moment more and more of the trees shook off their robes of snow. Soon, wherever you looked, instead of white shapes you saw the dark green of firs or the black prickly branches of bare oaks and beeches and elms. Then the mist turned from white to gold and presently cleared away altogether. Shafts of delicious sunlight struck down onto the forest floor and overhead you could see a blue sky between the tree-tops. (11.30)
The entire land of Narnia is changing in response to Aslan's presence. Think of it as time-lapse photography in the real world for a whole country.
They had been just as surprised as Edmund when they saw the winter vanishing and the whole wood passing in a few hours or so from January to May. They hadn't even known for certain (as the Witch did) that this was what would happen when Aslan came to Narnia. But they all knew that it was her spells which had produced the endless winter; and therefore they all knew when this magic spring began that something had gone wrong, and badly wrong, with the Witch's schemes. (12.2)
Like Edmund's transformation from traitor to hero, the switch from winter to summer in Narnia is virtually instantaneous, with no real spring or intermediate stage in-between.
"Hand it to me and kneel, Son of Adam," said Aslan. And when Peter had done so he struck him with the flat of the blade and said, "Rise up, Sir Peter Fenris-Bane." (12.27)
Aslan knights Peter in order to recognize his transition from boy to warrior. The actual knighting ceremony doesn't cause the transformation – it just makes it official.