Lenses are used in refracting telescopes and mirrors are used in reflecting telescopes. The mirrors are ground and polished so that a precise concave surface remains to be coated with a shiny, reflective finish. Mirrors concentrate light and focus all colors of the spectrum in an image. No lens can bring to focus all of the colors in white light. Further, lenses absorb some of the light that passes through, thus weakening the image. Mirrors are easier to make in large sizes than lenses and can concentrate the light of the dim images from deep space. Reflecting telescopes are currently used for space exploration.
This interactive explores reflecting telescopes. The large glass mirrors of modern reflectors have opened our door to the universe - and, as telescopes grow larger, the door opens wider. Learn how telescopes work and see the universe through different sized lenses.
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