Summary
Highlights
Telescopes have been crucial tools for stargazers since the 1600s, enabling us to see distant objects in detail. The challenge for our eyes is that distant objects appear smaller and darker. Telescopes overcome this by gathering more light and increasing the apparent size of objects.
The first telescope, invented around 1608 by Hans Lippershey, used lenses. These refractors use a convex objective lens to bend parallel light rays to a focal point, where the image is inverted. An eyepiece lens then magnifies this virtual image. The largest refracting telescope has an objective lens over 1 meter in diameter but suffers from light loss due to reflection.
Reflecting telescopes use curved mirrors instead of lenses. A concave mirror reflects parallel light rays to a focal point. A secondary mirror often deflects the image sideways to prevent obstruction, and an eyepiece lens magnifies it. Mirrors are easier to make in large sizes than lenses and avoid light loss from reflection. The Grand Telescopio Canarias is a large reflector at 10.4 meters in diameter, and even larger ones are under construction.
Atmospheric distortion makes stars twinkle and blurs images. To counteract this, research telescopes are often placed on mountaintops where the air is thinner or launched into space. The Hubble Space Telescope, a reflector launched in 1990, operates in the vacuum of space, providing incredibly clear images, equivalent to seeing a firefly in Tokyo from New York City.
While the video focuses on optical telescopes, other types exist, such as the Spitzer Space Telescope with infrared cameras and the Kepler telescope, which uses sensitive photometers to detect exoplanets. Telescopes have evolved immensely in 400 years, from basic three-times magnification to revealing distant galaxies in remarkable detail.