Christiaan Huygens’ Telescope Lenses Inform Us He Was Nearsighted


A world-famous Seventeenth-century astronomer credited with discovering Saturn’s moon Titan might have wanted glasses, based on a latest paper within the Royal Society Journal of the Historical past of Science.

In an period when telescope expertise was lower than a century previous, and evolving quickly via trial-and-error iterations, Christiaan Huygens was recognized for producing lenses of unparalleled high quality. Nevertheless, the telescopes he constructed with these lenses persistently underperformed. The trigger, AIP researcher Alex Pietrow suggests, might have been myopia, or nearsightedness, which was a typical situation within the Huygens household, although his case will need to have been gentle sufficient to not discover.

“As a result of Huygens didn’t want eyeglasses in day by day life like his father,” says Pietrow, “he most likely didn’t give it some thought when making telescopes. So he unconsciously included this eye defect into his designs.”

How do we all know Huygens was nearsighted? We don’t for certain: diagnosing medical situations in historic figures is difficult enterprise, and claiming to take action with certainty is just about malpractice in two professions – drugs and historical past. So Pietrow rightfully hedges his prescription with the suitable diploma of uncertainty. However he makes a robust case by analyzing the mathematical formulation Huygens developed by way of trial-and-error to grasp the physics of optics, and evaluating them to fashionable formulation. The telescopes Huygens constructed utilizing his formulation ended up with inferior resolving energy in comparison with a few of his contemporaries, and is likely to be defined if he was unconsciously accounting for his personal impaired eyesight.

Pietrow provides a number of different attainable explanations for the underperformance of Huygens’ telescopes, some extra believable than others. For instance, if Huygens’ telescope lenses suffered from sharpening errors, it will produce an identical discount in resolving energy. With out doing a take a look at known as a wavefront measurement on one in every of Huygens’ surviving lenses, this will’t altogether be dominated out, however Pietrow believes that is an unlikely rationalization, as a result of by all accounts Huygens’ lenses have been distinctive. For instance, in 1846 Frederik Kaiser, former director of the Leiden Observatory, described Huygens’ lenses as ‘pristine’. Huygens’ contemporaries would have been hard-pressed to enhance on his strategies, and he wouldn’t have been eager to share his strategies with them both.

“Within the time of Huygens, lens making was a really secretive artwork,” Pietrow advised Universe In the present day. “Totally different lens makers competed to be the most effective, whereas preserving their strategies secret. Which means that sharpening the lenses, sourcing the glass, and many others. have been all commerce secrets and techniques that no-one talked about.”

Christiaan Huygens, by Bernard Vaillant (1686). Credit score: Wikimedia Commons.

A 3rd risk, and maybe a extra believable one, is that Huygens purposefully constructed his telescope lenses with a shorter focus than mandatory – a ‘sub-optimal’ design alternative – however one which supplied one key benefit. It allowed the overall telescope size to be considerably shorter.

This was an essential benefit, as a result of the most effective telescopes of the interval have been reaching unwieldy lengths, some reaching over 50 meters from finish to finish.

The rationale for his or her extreme size was the necessity to right for what is named chromatic aberration.

When gentle passes via a lens that’s thicker within the center and thinner on the perimeters, the sunshine is bent, however totally different wavelengths are bent at totally different angles. Quick wavelengths, like people who produce the colour blue, will converge extra shortly than longer reddish wavelengths, leaving an annoying colourful tinge surrounding no matter object you’re via the telescope.

Gentle chromatic aberration seen across the fringe of the Moon. Credit score: Wikimedia Commons, Bishalsonar47.

The eventual resolution to chromatic aberration was to make use of mirrors moderately than glass – that is how Isaac Newton constructed his telescopes – a method that bypassed the issue altogether. However Huygens’ employed a unique resolution, and that was to extend the size of his telescopes, which additionally considerably lowered the results of chromatic aberration.

The draw back was that it made his telescopes impractically giant.

The truth is, Huygens’ largest telescopes have been so troublesome to make use of that he made most of his essential discoveries utilizing smaller ones. The telescope Huygens used to find Titan was solely 3.6m (12ft) lengthy, and utilizing both the identical 3.6m telescope or a brand new 7m (23ft) one, he was the primary to discern that Saturn’s odd look was as a result of a sequence of rings.

Huygens with one in every of his ‘Tubeless’ Aerial Telescopes. Credit score: Wikimedia Commons.

Within the battle in opposition to chromatic aberration, Huygens might have purposefully diminished his lenses’ functionality with a view to cut back the general size of his devices.

Nonetheless, Pietrow thinks that it’s unlikely that Huygens’ would deliberately introduce such an error into his devices. “We all know,” he writes, “that Huygens was making an attempt to make the optimum telescope.” For Pietrow, that leaves imaginative and prescient impairment because the most definitely remaining different.

No matter whether or not prescription glasses may need helped Huygens see the Universe somewhat clearer or not, the person undoubtedly helped the remainder of humanity see it extra clearly. He left behind a scientific legacy upon which astronomers and mathematicians are nonetheless constructing, and somewhat little bit of myopia, if it existed, didn’t get in the best way.

Study Extra:

Alex Pietrow, “Did Christiaan Huygens want glasses? A research of Huygens’ telescope equations and tables.” Royal Society Journal of the Historical past of Science.

Eyeglass prescription for Christiaan Huygens after 330 years.” AIP.

Featured Picture: A set of lenses by Christiaan Huygens together with his portrait within the background. Credit score: Rijksmuseum Boerhaave, Leiden.

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