Q1.
Do you remember learning about the use of telescope in the chapter ‘Beyond Earth’ in Curiosity, Grade 6?
Answer
Yes. In 'Beyond Earth' a telescope was introduced as the instrument that lets us see faint and distant objects in the sky — planets, moons and stars — far better than the unaided eye can.
What this chapter adds is how most modern telescopes do it. They are reflecting telescopes: the light-collecting element is a large concave mirror, not a lens.
Why a concave mirror is the right choice: a distant star is so far away that its light arrives as a parallel beam, and a parallel beam is exactly what a concave mirror concentrates to a point. The bigger the mirror, the more of that faint starlight it gathers, so the image is brighter and finer detail can be seen. A mirror can also be supported from behind over its whole area, so it can be built very large without sagging — which is much harder to do with a lens.