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Information on Reflecting Telescopes

The reflecting telescope was first invented in the 17th century, when scientists began to search for a more practical and accurate option than the refracting telescope. Reflecting telescopes have maintained their popularity since this time, although some alterations have been made to the original design. One of the modern alterations is the ability for computers to alter the angle of the telescope precisely. The two most common types of reflecting telescope are the Newtonian telescope and the Cassegrain telescope.

Origins
- Refracting telescopes were commonly used before the invention of the reflecting telescope. These telescopes featured a convex lens which focused light to a point, in a way similar to a magnifying glass. Italian inventor Niccolo Zucchi produced one of the first reflecting telescopes in the early 17th century. However, his invention needed improvements as the technology used for creating the primary curved mirror was crude. A secondary mirror inside Zucchi's telescope also blocked a portion of the incoming light. Much of the credit for inventing the reflecting telescope that we are familiar with is attributed to Sir Isaac Newton, who built his model in 1668. The advantages of the reflecting telescope over the earlier refracting models include clearer images, fewer lenses to clean, a shorter tube and a reduced cost of materials. Further improvements were made by Guillaume Cassegrain, whose model used similar principles to Newton's.
How the Newtonian Telescope Works
- Light enters the Newtonian telescope from a lens at the front of the telescope tube. This light is directed onto a convex mirror at the rear of the tube. The convex mirror focuses light to a point on a smaller, flat mirror at a 45 degree angle to the first, directing the light from the back of the tube to a viewing lens on top of it.
How the Cassegrain Telescope Works
- The Cassegrain telescope works in a similar way to the Newtonian telescope. The difference is that once light has been reflected from the first convex mirror at the back of the tube, a smaller convex mirror directs the light back to a small point behind the first mirror where there is a lens to view the image.
Usage
- The basic principles behind the reflecting telescope are used in modern telescopes, both optical and infrared, today. One of the main differences in those used today, however, is that the first, large convex mirror is usually coated with a thin layer of aluminum. Reflecting telescopes that are being used today include the two large Keck telescopes at the W. M. Keck Observatory in Hawaii. Each contains mirrors that measure more than 32 feet in diameter. These individual telescopes were the second largest in use in 2011. The Gran Telescopio Canarias was built in the Canary Islands in 2009, and is even bigger, with mirrors measuring more than 34 feet in diameter. However, smaller reflecting telescopes are also used by amateur astronomers.

Astronomy