While Galileo Galilei was not the first person to make or use a telescope, he was the first one to use it to observe the skies.
That’s why he is the name you probably hear most when it comes to the history of telescopes.
Astronomy grew rapidly based on Galileo’s observations and findings. He was also instrumental in confirming the heliocentric (sun-centered) model of the solar system that Copernicus had proposed.
Today, we thank Galileo and other scientists such as Johannes Kepler, Isaac Newton and Laurent Cassegrain for the vast advances in telescope design and the resulting cosmic discoveries.
Who Made the First Telescope?
It’s not surprising that the first telescopes were made by eyeglass makers. Both glasses and telescopes are, after all, heavily dependent on lenses.
The history of who invented the telescope first is murky, with several Dutchmen claiming recognition around the same time.
But it was Dutch spectacle maker Hans Lippershey, who in 1608 filed the first patent for a refracting telescope to the Netherlands government. So he is recognised as the first person to make a telescope.
His telescope could magnify things three times. Notably, it was only used for terrestrial observations. It wouldn’t be until Galileo built his own telescope that the first sky observations were made with a telescope.
Galileo got to work designing and making a refracting telescope as soon as he heard about the work the Dutchmen were doing, specifically the Dutch perspective glass that was used to magnify objects.
After showing off his invention and being appointed a lifelong university lecturer as a reward, Galileo got busy refining his telescope and discovering the skies.
The main thing he did was increase magnification, eventually making a telescope with 23x power. With it, he made several discoveries regarding the solar system.
He observed mountains and craters on the moon, saw the phases of venus, and discovered the Galilean moons – the four largest moons of Jupiter.
He also confirmed the Copernicus theory of a Heliocentric solar system.
Galileo’s invention was named a ‘telescope’ in 1911 (from Greek meaning far-seeing) and today it’s referred to as the Galilean telescope.
Who Invented the Modern Refracting Telescope?
Today’s refracting telescopes do not use the Galilean design. Instead, they have a modified Keplerian design.
They are named after the German astronomer Johannes Kepler.
Galileo designed his telescopes with a convex objective lens and a concave eyepiece lens.
Johannes Kepler designed a refracting telescope that was much longer (resulting in a longer focal length) and used two convex lenses for the objective and eyepiece.
The result was a much bigger field of view, though the images appeared upside down and were oriented the other way left to right.
But the wider field of view was a big enough improvement that the Keplerian telescope replaced the Galilean telescope up to date.
Good to know: The first big discovery with a Keplerian telescope was Titan, the largest moon of Saturn. It was made by Christiaan Huygens. He also improved our understanding of Saturn’s ring system.
When Was the Reflecting Telescope Discovered?
Refracting telescopes were great but they had two major limitations: chromatic aberration (a lens reflecting different colours of light at different angles) and spherical aberration (failure of a spherical lens to focus parallel light rays to a single focus point).
This resulted in degraded image quality, usually blurring.
While many scientists, including Galileo, had discussed and written about using mirrors in place of lenses, it was Isaac Newton who actually built the first reflecting telescope.
The main motivation among scientists for using mirrors to reflect light was to solve the chromatic and spherical aberrations that were seen in telescopes with lenses.
Newton built the first reflecting telescope in 1668, and that design is today known as the Newtonian telescope.
The Newtonian design consists of a primary reflecting mirror and a secondary angled mirror that reflects light from the primary mirror to an eyepiece mounted on the side of the telescope tubing.
Laurent Cassegrain, a Catholic priest, designed a variation of the reflector telescope.
Instead of a secondary mirror that reflected light to an eyepiece on the side of the telescope, he used a convex secondary mirror that reflected light back through a hole in the primary mirror and onto an eyepiece.
The main advantage of a Cassegrain telescope is its ability to produce high magnification in a compact design.
Even today, Cassegrain telescopes are popular for their compact and portable design.
After the Newtonian and Cassegrain telescopes, the following decades involved designing bigger and bigger telescopes to try and see more objects in the sky.
Astronomers discovered additional moons and William Parsons used a large 72-inch aperture reflector to discover that galaxies are spiral.
There were also many improvements to the refractor telescope, particularly attempts to correct spherical and chromatic aberrations.
After many years, achromatic lenses were eventually discovered, which mitigated these optical problems.
But because lenses were just too heavy and expensive, refractor telescopes could not be made as big as reflectors. Even modern refractor telescopes tend to be smaller than reflector telescopes.
Today, telescopes have gone beyond collecting just light from the sky.
We have radio telescopes that collect radio waves, infra-red telescopes, ultraviolet telescopes and X-ray telescopes that work from outside earth’s atmosphere.
But refracting and reflecting telescopes are still the most popular ones among amateur astronomers. If you need more help figuring out the difference between the two types and how they work, below is a quick explainer video.
Jack Bennett is the founder and editor of Stargazing in the UK. He lives in London and have started this blog about stargazing and amateur astronomy for beginners to keep track of his attempts to explore the Universe.