Mirror Telescopes

Before the use of mirror telescopes, many scientists studied the universe using a refracting telescope. A refracting telescope is made using a lens, while the reflecting telescope uses a mirror. People have been studying the use of curved mirrors as lenses as far back as the 11th century. The first functional and practical reflecting telescope was not built until the late 17th century by the famous scientist, Isaac Newton.

By focusing the light, the mirror in the telescope forms an image visible through the eyepiece. The shape of the mirror is usually parabolic. Most reflecting mirrors are utilized to observe objects in space. The light traveling from these objects are parallel rays, which can only be reflected by a mirror with a parabolic shape.

More scientists and astronomers use reflecting telescopes because there is hardly any chromatic aberration. In refracting telescopes, images with many colors of different wavelengths come out looking blurry because the lens cannot focus all the colors. A mirror reflects all wavelengths the same way. It is also cheaper to make. The objective mirror is only on one side so making large telescopes is not a problem. Telescope builders can use the backside to support the large objective. Whereas in the refracting telescope, the builder needs to figure out a way to support the lens with out obstructing paths of light that hit the lens.

Well-known reflecting telescopes are the Hale and Keck telescopes with objective mirrors 5 and 10 meters in diameter, respectively. It is said that reflecting telescopes that are ground-based are being built now. These telescopes will bring images that are greater than even images of the Hubble Space Telescope.