Final answer:
Reflecting telescopes use mirrors, while refracting telescopes use lenses. Reflecting telescopes are preferred in astronomy due to their ability to produce sharper images and avoid flaws in the glass. Refracting telescopes are usually more expensive because both sides of the lenses need to be accurately polished.
Step-by-step explanation:
A reflecting telescope uses mirrors, while a refracting telescope uses lenses. The main difference between the two types of telescopes is how they focus light. In a refracting telescope, light enters through a lens at the top and is focused near the bottom of the telescope. An eyepiece then magnifies the image so it can be viewed. In a reflecting telescope, light enters through an open end and is reflected by a mirror at the bottom, which then focuses the light at the top end of the telescope.
Refracting telescopes are traditionally more expensive because the lenses need to be polished to great accuracy on both sides, while only the front surface of a mirror needs to be accurately polished in a reflecting telescope. However, reflecting telescopes have some advantages over refracting telescopes. Since the light reflects off the front surface of the mirror in a reflecting telescope, flaws and bubbles within the glass do not affect the path of the light. Reflecting telescopes also tend to produce sharper images. For these reasons, most astronomical telescopes today use a mirror rather than a lens, making reflecting telescopes the preferred choice in the field of astronomy.