What is the speed of waves affected by?

How does refraction lead to the formation of an image by a convex/converging lense?

Will a more powerful lens have a curvy surface of a less curvy surface?

What is the equation for calculating the power (in dioptres) of a lens?

Why does light from astronomical objects reach Earth as effectively parallel sets of rays?

What are the features of a simple optical telescope?

What are the optical elements of a telescope?

What is the equation for calculating the angular magnification of a telescope?

Why do most astronomical telescopes have concave mirrors, not converging lenses, as their objectives?

How do concave mirrors bring a parallel beam of light to a focus?

Why are large telescopes needed to collect weak radiation from very distant sources?

What is diffraction?

How can diffraction be increased?

Why does the aperture of a telescope have to be very large?

How can a spectrum be produced by refraction in a prism?

How else can a spectrum be produced?