The first optical instruments with which the heavens were explored were large telescopes similar to the one first developed in Holland in 1608 and perfected by Galileo.

It was Sir Isaac Newton who replaced the lenses with mirrors. A large concave mirror placed at the foot of the tube reflects a portion of the sky and magnifies it. A second mirror receives this image and projects it to the eye. The wider the concave mirror, the brighter the image.

Today, the world’s largest mirror telescope is at Zelenchukskaya in the Caucasus Mountains in Russia. The main mirror is 6 meters in diameter. It weighs 70 tons and it took 16 years to build the telescope.

Such a large telescope in equipped with complicated machinery to maneuver it with precision. The telescope is placed inside a large dome which can revolve on special tracks. This allows it to scan the entire sky. The magnification, or the apparent increase in the size of the object examined, depends on the distance that can by regulated between the mirror and the focus. The luminosity, or brightness, of the image depends on the energy emitted by the image which is increased by the size of the mirror. The objects brought into focus can be photographed or observed directly.

The radiotelescope is completely different and is used in radioastronomy. These huge, delicate instruments consist basically of an antenna, or aerial, that picks up radio waves produced by the Sun, the stars or the galaxy. One of the best known examples is at Jodrell Bank.