By Emily Levesque, University of Washington
Who do we think of when asked, “Who invented the telescope?” For most of us, the first answer is probably Galileo Galilei, the famous Italian astronomer, in 1609. However, the first person to file a patent for the invention of a telescope was a German-Dutch spectacle maker named Hans Lippershey, in 1608. Let’s learn more.
Comparing Telescopes
The early telescopes by Hans Lippershey were small spyglass-like objects held in an astronomer’s hands. Used famously by Galileo, they looked like something a pirate might press to their eye in a Hollywood movie: a small tube with two lenses at either end using the power of refraction, the bending of light as it passes through something like a piece a glass, to magnify distant objects. The principal was simple and elegant, but refractive telescopes like this are only rarely used today.
Compare the first refractive telescopes to one of the most powerful telescopes today. This is one of the Keck telescopes on the summit of Mauna Kea in Hawaii. At a glance, it might seem utterly unrecognizable, but we can identify a common element between the two: light is focused and magnified by curved pieces of glass set in a line.
The starkest differences between the two types of telescope designs are, first, their glass elements: instead of using lenses to refract light, Keck—and most modern telescopes—uses mirrors to reflect and focus light; and, second, their size—the Keck telescope’s main mirror is 10 meters across or nearly 33 feet in diameter!
Lippershey may have kicked off the invention of the telescope, but when considering the telescopes we use today, there is arguably no better person to credit as the father of the modern telescope than a man named George Ellery Hale.
Problems in Building Telescopes
To understand why the small spyglasses of the 17th century have evolved into the enormous building-sized telescopes of today, we need to understand the two main goals of a good telescope. Telescopes need to produce images of distant objects that are both bright and sharp. For both of these goals, larger telescopes are better.
A big lens or mirror can collect much more light from dim objects. A big lens or mirror can also better focus that light into a sharper image. The ability of these mirrors to capture bright, sharp images allows us to see better and farther into space—similar to the way a large telephoto lens used by wildlife and sports photographers allows them to get sharp, close-up images of distant animals or athletes.
When it comes to building telescopes, however, size quickly becomes an incredible challenge. Engineering perfect large lenses is extremely difficult. The glass can’t have any imperfections or bubbles, and even gravity becomes an enemy. Lenses can only be supported at their edges so that nothing will block the light passing through the glass, and for large lenses, the very weight of the glass itself will distort the lens as it sags and succumbs to gravity.
This article comes directly from content in the video series Great Heroes and Discoveries of Astronomy. Watch it now, on Wondrium.
Optical Challenges
The optics of refraction also introduce several substantial challenges when admiring the image from a refracting telescope. To take just one example, light at different wavelengths focuses at different points, a phenomenon known as chromatic aberration. This happens because light’s index of refraction—how severely it bends when passing from air into a denser medium, like glass—depends on its wavelength or color.
Blue light bends more as it passes through glass, and therefore will come to a focused point at a different place along the optical axis relative to red light. Combined, this creates an image that looks slightly blurry to us, thanks to light with different wavelengths focusing in slightly different spots.
Newtonian Telescopes
Building very large refractive telescopes quickly proved prohibitively challenging. Instead, a solution was offered in the form of reflecting telescopes, using mirrors instead of lenses to focus the light.
The idea that curved mirrors behaved like lenses can be traced back to the 11th century and the work of Arabic mathematician Hasan Ibn al-Haytham—also known by the name Alhazen—and his work later spurred early telescope builders to replace the fickle and difficult lenses with mirrors instead.
James Gregory published a design for a reflecting telescope in 1663, and Isaac Newton is widely credited with building the first reflecting telescope in 1668, using a curved, polished piece of metal shaped like a segment of a sphere for his primary mirror, and a flat secondary mirror that could bounce the light reflected from the primary into an eyepiece. Today, we call such a design a Newtonian telescope. Still, Newton’s first telescope was tiny, with a main mirror only two inches across.
Mirrors ultimately made the construction of large telescopes easier, but it took centuries to refine the reflective telescope design from the polished copper and tin mirrors of the 1600s to the modern mirrors we use today. By the beginning of the 20th century, telescope builders had perfected the art of crafting parabola-shaped mirrors, improving the quality of the image. The mirrors themselves were now built out of thick glass and coated with silver.
Common Questions about the History of the Telescope
When Hans Lippershey first invented the telescope, it looked like what one might see a pirate use in a Hollywood movie. It was a small tube with two lenses at either end, using the power of refraction to magnify distant objects.
The two main goals of a good telescope are to produce images of distant objects that are both bright and sharp.
Isaac Newton is widely credited with building the first reflecting telescope in 1668, using a curved, polished piece of metal shaped like a segment of a sphere for his primary mirror, and a flat secondary mirror that could bounce the light reflected from the primary into an eyepiece. Today, we call such a design a Newtonian telescope.
