Yeats looks up and is thrown by the sight of a wintry sky, suddenly overcome by an inpouring rush of memory, emotion, awareness of life’s vitality and finiteness, and, despite the louring weather and death worries, he is  ‘riddled with light’. 

Suddenly I saw the cold and rook-delighting heaven …

I like the image of Heaven loving the rooks which score its expanse with their flight.   

The full poem can be read on the Poetry Foundation, here. 

Source: Yeats, ‘The Cold Heaven’, quoted and analysed in Seamus Heaney, Finders Keepers: Selected prose 1971-2001 (London: Faber and Faber, 2003), p. 317