Answer:
Sleeping during the day, I hide away. Watchful through the night, I open at dawn's light. But only for the briefest time, do I shine. And then I hide away. And sleep through the day.
Both old people and owls are said to be possessing this trait
I am a span of time you can always see through I am also the timepiece with the most pieces. What am I?
A harvest sown and reaped on the same day in an unplowed field. Which increases without growing, remains whole though it is eaten within and without. Is useless and yet the staple of nations.
By Moon or by Sun, I shall be found. Yet I am undone, if there's no light around
What do you purposefully put lots of in and on your body, but run away from when you encounter it outside?