Tradução: "The sun grow duller" e "Darkening sky"

So, I travelled, stopping now and again, in great steps of a thousand years or more, waiting to know what happened to the Earth. I watched, with a strange interest, the sun grow larger and duller (1) in the western sky, and the life of the old Earth die away. At last, more than thirty million years from now, the enormous red sun covered almost a tenth of the darkening sky (2).

1- Ficar maior e menos brilhante?
2- Consigo entender dark sky (o céu escuro) e darkened sky (o céu escurecido) nessa frase, mas não entendo por que ser the darkening sky (o céu que escurecia).

FONTE:
WELLS, H.G. The Time Machine. Penguin Readers Level 4. Pearson Education, 2008, p. 61.