Mirror Telescopes

Mirror telescopes are reflective devices extremely important in the world of science. From the early crude beginnings of mirror telescopes in 1616 to today's liquid mirror telescopes, a great advance in technology has been developed.

Sir Isaac Newton in 1668 was the first to create a very practical mirror telescope. It is based on reflection and collection of light rays. Because the light rays from the moon, stars, sun, and planets are parallel rays, the collection mirror needs to be a parabolic shape. This helps to focus rays to a single point. Long ago in the 10th century, amphitheaters were built in this shape so the audience could focus on the stage. Lighthouses and satellite dishes collect signals using this same shape. There are other derivations using various shaped mirrors in telescopes but the parabolic shape is the most common.

The composition of the material used for mirrors has changed throughout history. At one time they were made from solid fused quartz. Early ones were heavy solid one piece mirrors and today it is very common to find sectioned lighter mirrors in the telescopes. Crystallized ceramic glass, Pyrex sheet glass, and even liquid glass made from mercury is found in telescope mirrors. The coating on the substance is the most important factor and needs to be smooth and very reflective.

Sometimes a series of mirrors are used in telescopes. Powerful images can appear with multiple use of mirrors. Size of the mirrors became a major issue. Some were over 8 meters long. Then the invention of the computer completely changed telescopes. Control of the telescopes can be done by computer and the astronomer who once had to climb heights to peer through the telescope now can do it in an office using computer controls. Remarkable progress has taken place.