Changing Planet

A Brief History of the Astronomical Telescope III: Newton and his Reflecting Telescope

The moon shot with a Questar-7 reflecting telescope, an instrument inspired by Newton's Reflecting Telescope. It measures 470 mm (18 3/4 inch) in length, and 180 mm (7 inch) in diameter. It has an effective focal length of 2433 mm. Shot on Galileo's 445th Birthday, Feb. 15, 2009, the "Year of the Telescope."


“Nature and Nature’s Laws lay hid in night.

God said, ‘Let Newton Be!’ And all was light.”

.                                                   — Alexander Pope.


Galileo died in 1642 after a turbulent career as a mathematician-astronomer-astrologer-natural philosopher. He had discovered the law of free fall, and the law of the pendulum. He had introduced the notion of inertia, and the concept of acceleration as a change in velocity. He had made a refracting telescope from a combination of lenses placed judiciously in a tube, and pointed it at the heavens. He had seen the visible universe explode in magnitude, and he had also seen craters, mountains and valleys on the moon; moons around Jupiter; and phases of Venus. And from his observations he had concluded that the earth was a planet orbiting the sun, a confirmation of the Copernican heliocentric theory. In facing his Inquisitors, however, he publicly (and wisely) recanted his teachings, and gave in to a Church hell bent on keeping the earth at the center of the universe. The celestial bodies — the moon, planets and stars — would all continue to revolve around a stationary earth. He would lose the battle for the heavens, but through his intellectual descendants he would ultimately win the war.

With the muzzling of Galileo science in Italy would settle into prolonged hibernation, but not until it spread out of Italy to the North — into France, Germany and England. Galileo was a strong advocate of experimentation, but never believed that terrestrial and celestial phenomena would be governed by the same natural laws, that natural law would be universal. He was convinced that physical laws could be described mathematically, but he used precious little mathematics in actually expressing his discoveries. One of his latter day pronouncements had been, “A mind more piecing than mine will come along…” He could never have known how prescient those words would be. On Christmas day of the same year that he died, in the distant English hinterland of Southern Lincolnshire, England, Isaac Newton was born. (A change from the Julian to the Gregorian Calendar in 1752 actually puts his birth posthumously on the rather ordinary day of January 4, 1643.) Galileo is rightly regarded as the ‘father of modern science,’ but it is Newton who is the consensus choice as the greatest scientist ever, and the ‘architect of the modern world.’

Woolsthorpe Manor in Southern Lincolnshire. Isaac Newton was born here on Christmas Day of 1642 on the Julian Calendar. (Photo by the author)


In October 1642, shortly before Isaac Newton was born, his father — also ‘Isaac Newton’ — passed away. When the child was only three, his mother, Hannah Ayscough, took a second husband, Barnabas Smith, the elderly rector of a church in nearby North Witham, but the pre-nuptial contract did not accomodate a stepson. Accordingly, the child was left in the care of his maternal grandmother at Woolsthorpe Manor, the house in which he was born. After a rudimentary education in grammar school in Grantham, he was recalled home to manage the family farm. But demonstrating to his mother that he would be an abject failure in running the farm, young Isaac was sent back to school for a year to prepare for university. In 1661 Newton matriculated at his uncle’s alma mater, Trinity College of Cambridge. (Cambridge and Oxford are federations of colleges.) The reclusive, secretive and irascible nature that he displayed as a child would characterize him through his long life, but it would be complemented by an unbridled curiosity, an intellectual independence and an unrivaled mathematical and physical intuition.

Annus mirabilus and Annus horribilus

By his third year at Cambridge, the unique agenda of study he had set for himself put him squarely on a course to push past all the mathematicians and natural philosophers of Europe. When the Bubonic Plague made it across the English Channel from the Continent in 1665, and began to ravage the population of London, the great British universities of Oxford and Cambridge, each 50 miles distance from London, were closed down. To add to the misery brought on by the pestilence, a devastating fire broke out, burning over half of London. For Newton, the next 18-months that he was away from Cambridge, sequestered in his home in Woolsthorpe, would be crucial for his discoveries. Years later he would recall,

“In the beginning of the year 1665 I found the…  Bionomial series. The same year in May I found the method of Tangents… and had the direct method of fluxions & the next year in January had the Theory of Colours & in May following I had entrance into ye inverse method of fluxions. And the same year I began to think of gravity extending to ye orb of the Moon & (having found out how to estimate the force with wch [a] globe revolving within a sphere presses the surface of the sphere) from Keplers rule of the periodic times of the Planets being in sesquialterate proportion of their distances from the center of their Orbs, I deduced that the forces wch keep the Planets in their Orbs must [be] reciprocally as the squares of their distances from the centers about wch they revolve… All this was in the two plague years of 1665-1666. For in those days I was in the prime of my age for invention & minded Mathematicks & Philosophy more then than at any time since.”

How ironic it is that England’s annus horribilus (‘horrible year’) would coincide with Newton’s annus mirabilus (‘miracle year’). He used his new understanding of optics in creating the first reflecting telescope.

In 1664 at the annual Stourbridge Fair in Cambridge, Newton had purchased a prism triangular in cross-section (60° prism), and passed a beam of sunlight through it. He noticed, as had experimenters in the past, that the white light came out separated into colors from red-to-violet.


Newton's 60° prism, preserved at Cambridge University's Whipple Museum of Science. (Photo by the author)


What others had earlier concluded was that white light was pure, but, in passing through different thicknesses of glass, it simply changed color — into red in passing through the thinner part of the glass… into violet from the thicker. Newton, however, held a second prism contiguous with the first, and saw that the colors converged, and the white light was restored. Finally, when he separated the prisms so that different colors from the first prism were made to pass through the second, they were simply bent, but no modification in colors resulted. What this suggested to Newton was that the white light was a composite of all the colors, and the prism was separating it into its components, its “refrangibilities.” Moreover, a lens, like a prism would cause the colors to converge at different points, that refracting telescopes had that inherent fatal flaw. Chromatic (or color aberration) could not be avoided. (It can be reduced by making telescopes of narrow and extremely long tubes, with lenses with very slight curvature. But this is not practical. The longer and thinner the telescope, the more difficult is it to wield, and the more reduction in brightness of the image occurs.)


Annotating his personal copy of his book 'Opticks' (1704) Newton entered an explanation of the cause of chromatic aberration, and the necessity to produce a reflecting telescope in order to avoid this blurring, especially in observing colored objects. "Speculum," to which he refers, is a type of bronze, a silvery reflective coating concocted from 67% copper and 33% tin. (Courtesy of the Wren Library, Trinity College. Photo by the author.)


In 1672 when Newton was 29, he would write his first scientific paper, communicating his theory on light and colors to Henry Oldenburg, Secretary of the Royal Society of London. And in the same year the first reflecting telescope would be presented by his Cambridge mentor, Isaac Barrow, to the Royal Society of London, smaller, and for its size considerably more powerful than the refracting telescope and devoid of any chromatic aberration.

LEFT. Sketch of Newton's Reflector. RIGHT. Replica of Newton's Reflector. (Courtesy of the Royal Society of London.)


The Hubble Space Telescope (HST) placed into orbit by a space shuttle 'Discovery' in 1990 is a descendant of Newton's reflector. NASA lists a few of the Hubble's specs as follows: Length: 13.5 m (43.5 ft); Diameter 2.4 m (7 ft 10 in); Focal length: 57.6 m (189 ft); Mass: 11, 110 kg (24,500 lb): Orbital altitude: 559 km (347 mi); Orbital period: 96-97 minutes; and Orbit speed: 7,500 m/s (25,000 ft/s). Detectors able to "see" in the optical, ultraviolet, and near-infrared regions of the electromagnetic spectrum.


What he discovered during the “Year of the Plague,” when he was just 23, comprises the core of what he published another 23 years later in his magnum opus, Philosophia Naturalis Principia Matematica, the book that would unify with exquisite mathematical rigor the physics of heaven and earth and provide a consistent framework for interrogating nature. Indeed the Principa would provide the very tools for the discovery of new physical laws. The event is cited, not only as the crescendo of the Scientific Revolution, but also as the beginning of the Period of the Enlightenment.

Roubiliac's statue of Isaac Newton, prism in hand, standing in the antechapel of Trinity College Chapel. (Photo by author)


In his epic work, The Prelude, William Wordsworth had this statue in mind when he reminisced about lying in his bed in his dorm room at Trinity:

“The antechapel where the statue stood
Of Newton with his prism and silent face,
The marble index of a mind for ever
Voyaging through strange seas of Thought, alone.”


I am deeply indebted to Lord Martin Rees, Master of Trinity, Astronomer Royal, and the former President of the Royal Society, and the staff of the Wren Library for allowing me to view Newton’s personal books and papers. I am also indebted to Prof. André Buys in Pretoria, South Africa, nuclear engineer and amateur telescope maker for inspiring me to write the series of blogs on the history of the astronomical telescope. The series will conclude with a fourth and final installment, revealing the first ever inventor of the astronomical telescope, a surprise!



Bulent Atalay, a scientist, artist and author, has been described by NPR, PBS and the Washington Post as a “Modern Renaissance Man.” He is the author of two successful books on the intersection of art, science and mathematics, with Leonardo, the pre-eminent Renaissance man, serving as the foil. His best selling book, "Math and the Mona Lisa," (Smithsonian Books, 2004) has appeared in 13 languages. Professor Atalay's academic background is in theoretical physics. He travels around the world lecturing at academic institutions and on cruise ships on the "A-subjects," art, archaeology, astrophysics, atomic physics and Ataturk, confessing that he knows much less about the "B-subjects," business, banking, biology and botany...He is the President of the Ataturk Society of America (ASA), dedicated to promoting Ataturk's ideals of science and reason over dogma and superstition, of a secular state with full equality of genders. For more details click on Bulent Atalay
  • Elizabeth Atalay (

    This is such a fascinating story! I love how you humanize the background of these major scientific discoveries and figures.

  • J

    Newton’s description of what he accomplished during the two plague years (1665-1666) is fascinating. I agree with Elizabeth the personal aspects you included about Newton and his discoveries are wonderful. Photographs and illustrations are excellent.

  • Paulo Carvalho

    Interesting and engaging story. Those who can not stop until the end. Excellent!

  • jeff mark romitman

    very interesting story. imagine what if no isaac newton was born? hmmm..what?

  • Hi Jeff,
    My feeling is that the sum total of Newton’s contribution is so immense that, if he had not lived and had not published the “Principia” (which almost happened), the level of science and technology and the quality of our lives would be about the the same as it was in the 18th century. With the Scientific Revolution science and technology became permanently coupled, dragging each other upwards. The Industrial Revolution was fueled by the Scientific Revolution of the 17th century, but foremost by the achievements of Newton. On the other hand, if Leonardo (1452-1519) had published his discoveries, and genuinely gifted individuals carried on with his work, we might have reached our present level of science and technology two hundred years ago. Newton (1642-1727) and Leonardo (1452-1519) are members of an extremely rarified strata of genius, ‘the transformative genius,’ only half-a-dozen others belong. (Another is Shakespeare.) They define entire fields.

  • Nobuaki Honda

    It is a most captivating story on Isaac Newton. An early part of his personal life fascinates me. Photographic presentations on the subject are simply outstanding.

  • sofia donenfeld

    The story of these two giants are most interesting but the BLOG in relation to them

  • Kyle Dahlem

    I truly enjoyed reading your blog. Your writing always inspires me to read and learn more. I look forward to the next installment.

  • Kostas Dialynas

    I am fascinated by the simple and understandable way you always explain the themes you describe.

  • Alison

    Great article. Super enjoyable for the novice like me. Thanks for a concise summary.

  • Emily McKhann

    What a fascinating, fabulous article!!! I can’t wait to share this with my daughters. Thank you, thank you!!!!!

  • Zaith

    I am deeply fascinated with the article. Newton’s discoveries are indeed wonderful.

  • Sofia Donenfeld

    From my point of view your Blog is puzzling and wonderful. Since I am a novice concerning Physics, my comment is as follows; Dear Prof Bulent Atalay I have to congratulate for your perseverance in researching the great Leonardo. I also wish to be able to read all your findings in the future. Good health and good luck you are a great asset for the world of to-day. God bless you!

  • 行動電源

    Hello. excellent job. I did not expect this. This truly is a fantastic story. Thanks!

  • 行動電源

    Hello. excellent job. I did not expect this. This truly is a fantastic story. Thanks!

  • Depinder Bharti

    .832 mm of sagitta ? 😮 , I am building one with 400 cm reflector , sagitta 6 mm

  • Depinder Bharti

    .832 mm of sagitta ? 😮 , I am building one with 400 cm reflector , sagitta 6 mm

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