Isaac Newton Didn't Invent the Reflecting Telescope Alone

It has been raining for weeks. Every walk turns into a small negotiation with puddles, step around this one, straddle that one, and in each flooded seam of sidewalk another sky sits waiting, upside down and a little torn at the edges. I stopped over one longer than I meant to. Was this it? The first mirror anyone ever had, not glass, not metal, just water that happened to be still.

I think the mirror might be one of the best things humans ever made. Not the flashiest. Just one of the best.

Rain puddle reflecting a blue sky and trees on a quiet walking path

Isaac Newton is widely credited with inventing the reflecting telescope. Royal Society records tell a more complicated story, one that starts with a Scottish mathematician's overlooked 1663 design and runs through a burned observatory in Danzig to a 6.5-meter mirror now orbiting a million miles from Earth. This is a short history of the mirror in astronomy, and of how one name ended up carrying credit that was never entirely his alone.

A Short Tube and an Argument About Color

Isaac Newton built his first reflecting telescope in late 1671. By February 1672, it had reached the Royal Society in London, a demonstration that didn't look like the start of anything, let alone the opening move in a three-and-a-half-century argument over glass and metal that would eventually put a mirror farther from Earth than any hand could ever reach. What struck the members first wasn't what the telescope showed. It was how you looked at it.

Instead of squinting down the length of a long barrel, you leaned in near the base, where a small angled mirror had already redirected the light for you. The mirror itself was metal, ground and polished, sitting inside a tube of paper or pasteboard, nothing built to survive a bad afternoon, never mind three centuries.

A reflecting telescope gathers and focuses light with a curved mirror instead of a glass lens. Because reflected light does not split into separate colors the way light bent through a lens does, a mirror-based telescope avoids chromatic aberration, the color-fringing problem that limited early refracting telescopes and pushed astronomers toward reflectors instead.

Newton had reason to care about that fringing problem specifically. Earlier that same year, he had sent the Society his theory of light and color: prism experiments showing that white light was made of every color at once, each one bending by a slightly different amount as it passed through glass. To someone who had just measured how unevenly a lens refracts violet light and red light, a telescope built with no lens at all wasn't a clever workaround. It was the theory, made physical.

The telescope came with its own paper trail. Royal Society records show that Secretary Henry Oldenburg had a drawing of the design made, asked Newton to review it, and then forwarded it to Christiaan Huygens in the Netherlands, a step historians read as an effort to help establish Newton's priority for the invention.

None of that paperwork mattered to the mirror itself. It just had to survive being metal, kept in a tube, in somebody's house.

Isaac Newton examining his early reflecting telescope in London in 1672 (artist's illustration)

What Burns When an Observatory Burns

A year after Newton's telescope reached London, a different kind of astronomer was making a similar case in his own way. Johannes Hevelius ran a brewery in Danzig, now Gdańsk, and also built some of the most detailed astronomical instruments of his century.

In 1673, he put both worlds on paper. His book Machina Coelestis didn't just describe his instruments, it illustrated them in careful detail, the kind of imagery historians now read as an argument in itself: look how precisely built this is, look how much you can trust what it measured, according to a Cambridge University Press analysis.

Six years after that book was printed, on the night of September 26, 1679, Hevelius's house burned. So did his brewery, his observatory, his library, and the print shop that had made that same illustrated book possible in the first place, Cambridge's record of the event shows.

There's something almost unfair about that. Years of precision aimed at objects thousands of light-years away, undone by a spark that started somewhere close to home.

Fifty years later, John Hadley's metal mirror was a study in the same fragility, handled a different way. It's still kept at the Royal Society today, preserved in a custom mahogany case built for storing and carrying it. Whatever the exact reasoning, somebody had decided a mirror this valuable needed a box, not a shelf.

By the early 1720s, astronomers had learned two separate lessons: how to shape a mirror, and how hard it is to keep one safe. Plenty happened to mirrors in the centuries between — that's a different chapter. It would take another three centuries, and a launchpad in French Guiana, before anyone tried sending a mirror into space at all. Getting it there, unfolding it, and aligning it from a million miles away would become its own kind of test.

Johannes Hevelius beside astronomical instruments during the 1679 Danzig fire (artist's illustration)

Credit, it turns out, has needed defending for about as long as telescopes have existed. Newton wasn't the last scientist to need a paper trail, and he wasn't the first either. Readers curious about a much later version of the same fight might recognize it in how the story of Hubble's law quietly left out Georges Lemaître for decades.

The Mirror That Had to Unfold Itself a Million Miles From Home

On December 25, 2021, a rocket left French Guiana carrying a mirror that didn't look like a mirror yet. It looked more like a folded piece of origami, wings tucked against its own frame, waiting to do something no engineer could physically supervise: unfold eighteen hexagonal segments in vacuum until they worked as a single curved surface 6.5 meters across, or 21 feet 4 inches, as NASA put it for anyone used to measuring rooms instead of telescopes.

Eighteen mirror segments had to align precisely enough to work as one. All of it, 1.5 million kilometers from Earth.

The design leaps past Newton's single angled mirror. NASA calls the arrangement a three-mirror anastigmat: light bounces from a concave primary mirror to a convex secondary, then to a tertiary that removes distortion and flattens the image. A fourth mirror, flat and small, makes the fine adjustments afterward that keep Webb precisely pointed at its target.

It doesn't orbit Earth at all. It loops around L2, a gravitational balance point well past the Moon, rather than sitting still there, staying in the shadow of its sunshield so the faint infrared light it's built to catch doesn't get lost in its own heat, per NASA's telescope overview.

Long before the era of space telescopes, craftspeople in the Andean Tiwanaku cultural tradition made polished mirrors of their own. The example held by the Smithsonian's National Museum of the American Indian is dated to roughly AD 500 to 1100. Webb's mirror serves a radically different purpose, but both objects depend on the same basic act: a controlled surface redirecting light. In a way, the mirror never really changed jobs. It just started serving a lot more people at once, through approved observing programs used by astronomers around the world.

By the following spring, NASA confirmed the eighteen segments were finally working as one continuous surface instead of eighteen separate pieces. What that milestone didn't settle is who actually gets credit for getting a mirror this far, because that question turns out to be a lot less tidy than the finished photograph suggests.

The telescope's name is still debated, for reasons that have nothing to do with optics — its own story about how NASA decided what to call its biggest telescope.

Tiwanaku mirror from the Andes dating to approximately AD 500 to 1100

Zoom out further, and the pattern holds well past one Danzig brewery: plenty of the people who actually built instruments like this one never made it into the record at all, a gap that runs especially deep in the history of women in astrophysics and cosmology.

The Man Who Didn't Invent It Alone

I'll be honest: I've told this story the easy way so far, mirror problem, mirror solution, in that order. It's not quite that clean.

Newton had a functioning reflecting telescope by 1672, but the idea behind it didn't start with him. The Royal Society credits James Gregory with proposing, in 1663, that a parabolic mirror could correct the distortion a simple curved mirror introduces on its own. Newton built the working instrument. Gregory had already done the math nine years earlier.

The tidier textbook line, that Newton invented the reflecting telescope, isn't false so much as it's incomplete. It compresses an idea, a working prototype, and decades of later refinement by people like Hadley into a single name, which is convenient and a little unfair to everyone else in the sentence.

A second popular version of this story is even less accurate: that mirrors simply replaced lenses once telescope-makers figured out the color problem. Webb's own design argues against that. It's still built around mirrors, a three-mirror imaging system plus a fourth for fine-pointing, but the finished instrument is closer to a system, mirrors, sensors, a sunshield, alignment hardware, than to a single elegant fix. Reflectors solved chromatic aberration. They introduced their own headaches around shape, alignment, and temperature control that engineers are still solving today.

The tidier version of this story would still be worth telling. It's just not quite the one the historical record supports.

Historical speculum metal mirror and mahogany case used for astronomical optics

Refracting telescopes, the lens kind, hit a wall fairly fast. Reach for sharper, farther objects and you need a bigger lens, which means more weight and more of that same color-splitting problem, multiplied. Johannes Hevelius handled it about as well as anyone could without a mirror: building telescopes over a hundred feet long, bracing lenses across open wooden frames just to get the magnification he wanted. It worked. By most accounts, it was also a nightmare to actually use.

Mirrors did what a longer tube couldn't, which is still why the largest observatories on Earth build around mirrors instead of glass. And in its own accidental way, that's what a rain puddle was doing too. Somewhere between a sidewalk and a spacecraft looping through space a million miles out, water and metal turn out to be doing roughly the same job: holding still long enough to hand a little bit of light back to whoever happens to be looking.

The same trade-off Newton and Hevelius were arguing over still sits on the shelf at every telescope shop: mirror or lens, aperture or magnification, and which number on the box actually matters. What to check before buying a first telescope →

James Webb Space Telescope using its 18-segment primary mirror to collect infrared light from distant galaxies

Frequently asked questions

Why does the James Webb Space Telescope orbit so far from Earth?

NASA positions Webb near the Sun-Earth L2 point, about 1.5 million kilometers (930,000 miles) from Earth. That distance lets its sunshield keep the instruments cold enough to detect the faint infrared light the mirror is built to collect.

Is the Tiwanaku mirror one of the oldest mirrors ever made?

No. Polished mirrors go back thousands of years before the Tiwanaku period, including obsidian mirrors made in Anatolia around 6000 BC. The Smithsonian's piece is best understood as an example from the Andean Tiwanaku cultural tradition, dated to roughly AD 500 to 1100, not as one of the earliest mirrors overall.

Why did the Royal Society send Isaac Newton's telescope design to Christiaan Huygens?

Henry Oldenburg had a drawing of Newton's design made and asked Newton to review it before sending it on to Christiaan Huygens in the Netherlands. Royal Society records describe the step as part of an effort to help establish Newton's priority for the invention.

How long did it take NASA to align the James Webb Space Telescope's mirror segments after launch?

Webb launched December 25, 2021. NASA announced on March 16, 2022 that the telescope had reached a major alignment milestone on March 11, with all 18 primary mirror segments working as a single optical surface, a little under three months after launch.

Sources & References

This article is for educational and informational purposes only. Sources are linked where available. Readers are encouraged to consult primary sources for further research.

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