The Archenhold Observatory's refracting telescope is a full 21 meters long. Looking through the powerful refractor opens up otherwise invisible worlds. The giant telescope, known by Berliners as the ...

The first telescopes used lenses, known as refracting telescopes. Small instruments – whether for amateur astronomers starting out or people keen to look at distant mountains or spy on their neighbors ...

The angle of incidence when the angle of refraction is 90 o, and the ray changes from just refracting to total internal reflection, is called the critical angle. The diagram below shows the light ...