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The Rest Is Science
The Rest Is Science

The Science of Putting Sunglasses on The Sun

August 09, 2026 • 1h 0m

Summary

⏱️ 8 min read

Overview

Michael Stevens and Hannah Fry tackle the whimsical yet surprisingly complex challenge of putting sunglasses on the sun. What begins as an absurd thought experiment evolves into a deep exploration of angular diameter, solar viewing safety, and real proposals for space-based solar management. The discussion reveals both the engineering challenges of creating such an illusion and genuine scientific concepts like space sunshades and solar mirrors that could have profound implications for Earth's climate.

The Initial Challenge: Angular Diameter and Viewing Distance

Michael and Hannah establish the fundamental physics behind making the sun appear to wear sunglasses. They explain angular diameter—how objects appear different sizes based on distance—and calculate that at arm's length, a pencil (0.65 cm wide) would cover the sun's disk. However, they quickly realize that merely covering 15-30% of the sun with sunglasses-shaped objects wouldn't be safe, as viewers would need to dim the sun by 100,000 times to avoid permanent retinal damage.

  • The sun takes up about 32 arc minutes (half a degree) in the sky
  • At arm's length (70 cm), an object only 0.65 cm wide (pencil-width) would completely block the sun
  • Safe solar viewing requires decreasing the sun's light by 100,000 times to avoid retinal sunburn
  • Looking at the sun delivers a million billion photons per second onto your retina
" You're probably sitting there thinking, putting sunglasses on the sun, that's never going to work. Why? Because the sun doesn't have ears or a nose that are going to fall right off. "
" 10 seconds of looking at the sun is the equivalent of dropping a double a battery right onto your retina from a foot up same amount of energy "

The Binocular Vision Problem

Hannah introduces a crucial complication: human eyes are about 6 centimeters apart, which dramatically affects how large the sunglasses need to be at various distances. At arm's length, accounting for both eyes requires sunglasses 7.5 cm wide rather than 0.65 cm. This discovery leads to the realization that the closer the viewing platform, the more dominant the eye-separation factor becomes, making single-eye viewing the only practical option at short distances.

  • Your pupil is about 4mm across, requiring sunglasses to be 10.5mm wide for full coverage of one eye
  • Human eyes are 6cm apart, requiring sunglasses to be 7.5cm wide for binocular viewing at arm's length
  • At short distances, eye separation becomes about 10% of the viewing distance, making binocular viewing impractical
  • The effect improves as distance increases because eye separation becomes a smaller factor
" I think the only way to get it to work at such a short distance would be closing one eye. "

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