When I was six, I asked my father why the sky was blue. He did not know. "I will find out," he said. That evening he came home with a book from the library. We sat at the kitchen table and he read slowly. Sunlight is not one colour, the book said. It is many colours together. When it enters the air, the small blue part spreads everywhere. So we see blue above us. I asked why the sky turns orange in the evening. My father turned the page. At sunset, the light travels a longer way through the air, he read. The blue is lost on the road. Only the red and the orange arrive. I did not understand every word. But I remember his finger under each line, and his voice, careful and slow. Yesterday my daughter asked me the same question. I told her I would find out. Then I opened the same book. It still has my father's notes in the corner.