An invention which has contributed greatly to the development of modern science is the telescope. This is an instrument for magnifying distant objects and making them appear to be closer. It has two essential parts. These are the objective which collects light from the distant object and forms a real image, and the eye piece which forms a magnified image of this image. Different types of telescopes function in different ways. For example, refracting telescopes use a convex lens as the objective. Reflecting telescopes, on the other hand, use a curved mirror with a large diameter as the objective.