Newton's Reflecting Telescope

Isaac Newton invented the reflecting telescope in 1668 to solve the severe chromatic aberration (color distortion) inherent in traditional refracting lenses. Lenses of the era split light into different colors, blurring the images of distant stars. By using curved mirrors instead of glass lenses, Newton's design completely bypassed this optical problem.

Newton's first functional reflecting telescope was surprisingly small, measuring only about 6.2 inches in length and 2.5 inches in diameter. Despite its tiny size, it could magnify objects by about 40 times. This compact design was a massive breakthrough compared to the unwieldy, dozens-of-feet-long refracting telescopes of the period.

The telescope used a primary concave spherical mirror at the back of the tube to gather light. The light was then reflected forward onto a smaller, flat mirror tilted at a 45-degree angle. This secondary mirror redirected the light out the side of the tube into an eyepiece, a design now universally known as a Newtonian reflector.

Newton's second, improved reflecting telescope, which he built in 1671, is currently preserved at the Royal Society of London. He famously presented this replica to the Royal Society to demonstrate his optical theories. It remains one of the most important artifacts in the history of scientific instrumentation.